diff --git a/ext/java/org/jruby/ext/stringio/StringIO.java b/ext/java/org/jruby/ext/stringio/StringIO.java
index fcabc4eb..ed929b54 100644
--- a/ext/java/org/jruby/ext/stringio/StringIO.java
+++ b/ext/java/org/jruby/ext/stringio/StringIO.java
@@ -95,9 +95,19 @@ static class StringIOData {
     private byte flags;
 
     // MRI: get_strio, StringIO macro
-    private StringIOData getPtr() {
+    private StringIOData getPtrForWrite() {
         // equivalent to rb_io_taint_check without tainting
         checkFrozen();
+
+        checkInitialized();
+
+        return ptr;
+    }
+
+    // MRI: get_strio, StringIO macro
+    private StringIOData getPtrForRead() {
+        checkInitialized();
+
         return ptr;
     }
 
@@ -143,7 +153,7 @@ public static RubyClass createStringIOClass(final Ruby runtime) {
 
     // mri: get_enc
     public Encoding getEncoding() {
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForRead();
         Encoding enc = ptr.enc;
         if (enc != null) {
             return enc;
@@ -158,7 +168,7 @@ public Encoding getEncoding() {
     }
 
     public void setEncoding(Encoding enc) {
-        getPtr().enc = enc;
+        getPtrForWrite().enc = enc;
     }
 
     @JRubyMethod(name = "new", rest = true, meta = true)
@@ -258,7 +268,7 @@ private static IRubyObject yieldOrReturn(ThreadContext context, Block block, Str
             try {
                 val = block.yield(context, strio);
             } finally {
-                strio.getPtr().string = null;
+                strio.getPtrForWrite().string = null;
                 strio.flags &= ~STRIO_READWRITE;
             }
         }
@@ -272,7 +282,7 @@ protected StringIO(Ruby runtime, RubyClass klass) {
 
     @JRubyMethod(visibility = PRIVATE, keywords = true)
     public IRubyObject initialize(ThreadContext context) {
-        if (getPtr() == null) {
+        if (ptr == null) {
             ptr = new StringIOData();
         }
 
@@ -284,7 +294,7 @@ public IRubyObject initialize(ThreadContext context) {
 
     @JRubyMethod(visibility = PRIVATE, keywords = true)
     public IRubyObject initialize(ThreadContext context, IRubyObject arg0) {
-        if (getPtr() == null) {
+        if (ptr == null) {
             ptr = new StringIOData();
         }
 
@@ -296,7 +306,7 @@ public IRubyObject initialize(ThreadContext context, IRubyObject arg0) {
 
     @JRubyMethod(visibility = PRIVATE, keywords = true)
     public IRubyObject initialize(ThreadContext context, IRubyObject arg0, IRubyObject arg1) {
-        if (getPtr() == null) {
+        if (ptr == null) {
             ptr = new StringIOData();
         }
 
@@ -308,7 +318,7 @@ public IRubyObject initialize(ThreadContext context, IRubyObject arg0, IRubyObje
 
     @JRubyMethod(visibility = PRIVATE, keywords = true)
     public IRubyObject initialize(ThreadContext context, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2) {
-        if (getPtr() == null) {
+        if (ptr == null) {
             ptr = new StringIOData();
         }
 
@@ -324,7 +334,7 @@ private void strioInit(ThreadContext context, int argc, IRubyObject arg0, IRubyO
         IRubyObject string = context.nil;
         IRubyObject vmode = context.nil;
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -412,7 +422,7 @@ public IRubyObject initialize_copy(ThreadContext context, IRubyObject other) {
 
         if (this == otherIO) return this;
 
-        ptr = otherIO.getPtr();
+        ptr = otherIO.getPtrForRead();
         flags = (byte) (flags & ~STRIO_READWRITE | otherIO.flags & STRIO_READWRITE);
 
         return this;
@@ -420,7 +430,7 @@ public IRubyObject initialize_copy(ThreadContext context, IRubyObject other) {
 
     @JRubyMethod
     public IRubyObject binmode(ThreadContext context) {
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
         ptr.enc = EncodingUtils.ascii8bitEncoding(context.runtime);
         if (writable()) ptr.string.setEncoding(ptr.enc);
 
@@ -479,7 +489,7 @@ public IRubyObject closed_p() {
     public IRubyObject close_read(ThreadContext context) {
         // ~ checkReadable() :
         checkInitialized();
-        if ( (getPtr().flags & OpenFile.READABLE) == 0 ) {
+        if ( (getPtrForWrite().flags & OpenFile.READABLE) == 0 ) {
             throw context.runtime.newIOError("not opened for reading");
         }
         int flags = this.flags;
@@ -499,7 +509,7 @@ public IRubyObject closed_read_p() {
     public IRubyObject close_write(ThreadContext context) {
         // ~ checkWritable() :
         checkInitialized();
-        if ( (getPtr().flags & OpenFile.WRITABLE) == 0 ) {
+        if ( (getPtrForWrite().flags & OpenFile.WRITABLE) == 0 ) {
             throw context.runtime.newIOError("not opened for writing");
         }
         int flags = this.flags;
@@ -616,7 +626,7 @@ public IRubyObject each_byte(ThreadContext context, Block block) {
         if (!block.isGiven()) return enumeratorize(runtime, this, "each_byte");
 
         checkReadable();
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -650,7 +660,7 @@ public IRubyObject each_char(final ThreadContext context, final Block block) {
     @JRubyMethod(name = {"eof", "eof?"})
     public IRubyObject eof(ThreadContext context) {
         checkReadable();
-        StringIOData ptr = getPtr();
+        StringIOData ptr = this.getPtrForRead();
         if (!isEndOfString()) return context.fals;
         return context.tru;
     }
@@ -660,7 +670,7 @@ private boolean isEndOfString() {
     }
 
     private boolean isOutside(int pos) {
-        StringIOData ptr = getPtr();
+        StringIOData ptr = getPtrForRead();
         return ptr.string == null || pos >= ptr.string.size();
     }
 
@@ -670,7 +680,7 @@ public IRubyObject getc(ThreadContext context) {
 
         if (isEndOfString()) return context.nil;
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -693,7 +703,7 @@ public IRubyObject getbyte(ThreadContext context) {
         if (isEndOfString()) return context.nil;
 
         int c;
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
         boolean locked = lock(context, ptr);
         try {
             c = ptr.string.getByteList().get(ptr.pos++) & 0xFF;
@@ -707,7 +717,7 @@ public IRubyObject getbyte(ThreadContext context) {
     // MRI: strio_substr
     // must be called under lock
     private RubyString strioSubstr(Ruby runtime, int pos, int len, Encoding enc) {
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForRead();
 
         final RubyString string = ptr.string;
         int rlen = string.size() - pos;
@@ -758,25 +768,25 @@ private static int bm_search(byte[] little, int lstart, int llen, byte[] big, in
 
     @JRubyMethod(name = "gets", writes = FrameField.LASTLINE)
     public IRubyObject gets(ThreadContext context) {
-        if (getPtr().string == null) return context.nil;
+        if (getPtrForWrite().string == null) return context.nil;
         return Getline.getlineCall(context, GETLINE, this, getEncoding());
     }
 
     @JRubyMethod(name = "gets", writes = FrameField.LASTLINE)
     public IRubyObject gets(ThreadContext context, IRubyObject arg0) {
-        if (getPtr().string == null) return context.nil;
+        if (getPtrForWrite().string == null) return context.nil;
         return Getline.getlineCall(context, GETLINE, this, getEncoding(), arg0);
     }
 
     @JRubyMethod(name = "gets", writes = FrameField.LASTLINE)
     public IRubyObject gets(ThreadContext context, IRubyObject arg0, IRubyObject arg1) {
-        if (getPtr().string == null) return context.nil;
+        if (getPtrForWrite().string == null) return context.nil;
         return Getline.getlineCall(context, GETLINE, this, getEncoding(), arg0, arg1);
     }
 
     @JRubyMethod(name = "gets", writes = FrameField.LASTLINE)
     public IRubyObject gets(ThreadContext context, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2) {
-        if (getPtr().string == null) return context.nil;
+        if (getPtrForWrite().string == null) return context.nil;
         return Getline.getlineCall(context, GETLINE, this, getEncoding(), arg0, arg1, arg2);
     }
 
@@ -800,7 +810,7 @@ public IRubyObject gets(ThreadContext context, IRubyObject[] args) {
         self.checkReadable();
 
         if (limit == 0) {
-            if (self.getPtr().string == null) return context.nil;
+            if (self.getPtrForWrite().string == null) return context.nil;
             return RubyString.newEmptyString(context.runtime, self.getEncoding());
         }
 
@@ -816,7 +826,7 @@ public IRubyObject gets(ThreadContext context, IRubyObject[] args) {
     private static final Getline.Callback<StringIO, StringIO> GETLINE_YIELD = (context, self, rs, limit, chomp, block) -> {
         IRubyObject line;
 
-        StringIOData ptr = self.getPtr();
+        StringIOData ptr = self.getPtrForWrite();
         if (ptr.string == null || ptr.pos > ptr.string.size()) {
             return self;
         }
@@ -839,7 +849,7 @@ public IRubyObject gets(ThreadContext context, IRubyObject[] args) {
         RubyArray<IRubyObject> ary = (RubyArray<IRubyObject>) context.runtime.newArray();
         IRubyObject line;
 
-        StringIOData ptr = self.getPtr();
+        StringIOData ptr = self.getPtrForWrite();
         if (ptr.string == null || ptr.pos > ptr.string.size()) {
             return null;
         }
@@ -871,7 +881,7 @@ private IRubyObject getline(ThreadContext context, final IRubyObject rs, int lim
             return context.nil;
         }
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
         Encoding enc = getEncoding();
 
         boolean locked = lock(context, ptr);
@@ -975,19 +985,19 @@ private static int chompNewlineWidth(byte[] bytes, int s, int e) {
     @JRubyMethod(name = {"length", "size"})
     public IRubyObject length(ThreadContext context) {
         checkInitialized();
-        RubyString myString = getPtr().string;
+        RubyString myString = getPtrForRead().string;
         if (myString == null) return RubyFixnum.zero(context.runtime);
         return getRuntime().newFixnum(myString.size());
     }
 
     @JRubyMethod(name = "lineno")
     public IRubyObject lineno(ThreadContext context) {
-        return context.runtime.newFixnum(getPtr().lineno);
+        return context.runtime.newFixnum(getPtrForRead().lineno);
     }
 
     @JRubyMethod(name = "lineno=", required = 1)
     public IRubyObject set_lineno(ThreadContext context, IRubyObject arg) {
-        getPtr().lineno = RubyNumeric.fix2int(arg);
+        getPtrForWrite().lineno = RubyNumeric.fix2int(arg);
 
         return context.nil;
     }
@@ -996,7 +1006,7 @@ public IRubyObject set_lineno(ThreadContext context, IRubyObject arg) {
     public IRubyObject pos(ThreadContext context) {
         checkInitialized();
 
-        return context.runtime.newFixnum(getPtr().pos);
+        return context.runtime.newFixnum(getPtrForRead().pos);
     }
 
     @JRubyMethod(name = "pos=", required = 1)
@@ -1009,13 +1019,13 @@ public IRubyObject set_pos(IRubyObject arg) {
 
         if (p > Integer.MAX_VALUE) throw getRuntime().newArgumentError("JRuby does not support StringIO larger than " + Integer.MAX_VALUE + " bytes");
 
-        getPtr().pos = (int)p;
+        getPtrForWrite().pos = (int)p;
 
         return arg;
     }
 
     private void strioExtend(ThreadContext context, int pos, int len) {
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1054,12 +1064,12 @@ public IRubyObject putc(ThreadContext context, IRubyObject ch) {
 
         checkModifiable();
         if (ch instanceof RubyString) {
-            if (getPtr().string == null) return context.nil;
+            if (getPtrForWrite().string == null) return context.nil;
             str = substrString((RubyString) ch, str, runtime);
         }
         else {
             byte c = RubyNumeric.num2chr(ch);
-            if (getPtr().string == null) return context.nil;
+            if (getPtrForWrite().string == null) return context.nil;
             str = RubyString.newString(runtime, new byte[]{c});
         }
         write(context, str);
@@ -1091,7 +1101,7 @@ private IRubyObject readCommon(ThreadContext context, int argc, IRubyObject arg0
 
         IRubyObject str = context.nil;
         boolean binary = false;
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
         int pos = ptr.pos;
 
         boolean locked = lock(context, ptr);
@@ -1187,7 +1197,7 @@ public IRubyObject pread(ThreadContext context, IRubyObject arg0, IRubyObject ar
     @SuppressWarnings("fallthrough")
     private RubyString preadCommon(ThreadContext context, int argc, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2) {
         IRubyObject str = context.nil;
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForRead();
         Ruby runtime = context.runtime;
         int offset;
         final RubyString string;
@@ -1294,6 +1304,8 @@ public IRubyObject readlines(ThreadContext context, IRubyObject[] args) {
     // MRI: strio_reopen
     @JRubyMethod(name = "reopen", keywords = true)
     public IRubyObject reopen(ThreadContext context) {
+        checkFrozen();
+
         // reset the state
         strioInit(context, 0, null, null, null);
         return this;
@@ -1302,7 +1314,7 @@ public IRubyObject reopen(ThreadContext context) {
     // MRI: strio_reopen
     @JRubyMethod(name = "reopen", keywords = true)
     public IRubyObject reopen(ThreadContext context, IRubyObject arg0) {
-        checkModifiable();
+        checkFrozen();
 
         if (!(arg0 instanceof RubyString)) {
             return initialize_copy(context, arg0);
@@ -1316,7 +1328,7 @@ public IRubyObject reopen(ThreadContext context, IRubyObject arg0) {
     // MRI: strio_reopen
     @JRubyMethod(name = "reopen", keywords = true)
     public IRubyObject reopen(ThreadContext context, IRubyObject arg0, IRubyObject arg1) {
-        checkModifiable();
+        checkFrozen();
 
         // reset the state
         strioInit(context, 2, arg0, arg1, null);
@@ -1326,7 +1338,7 @@ public IRubyObject reopen(ThreadContext context, IRubyObject arg0, IRubyObject a
     // MRI: strio_reopen
     @JRubyMethod(name = "reopen", keywords = true)
     public IRubyObject reopen(ThreadContext context, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2) {
-        checkModifiable();
+        checkFrozen();
 
         // reset the state
         strioInit(context, 3, arg0, arg1, arg2);
@@ -1337,7 +1349,7 @@ public IRubyObject reopen(ThreadContext context, IRubyObject arg0, IRubyObject a
     public IRubyObject rewind(ThreadContext context) {
         checkInitialized();
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1370,7 +1382,7 @@ private RubyFixnum seekCommon(ThreadContext context, int argc, IRubyObject arg0,
             whence = arg1;
         }
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         checkOpen();
 
@@ -1405,8 +1417,7 @@ private RubyFixnum seekCommon(ThreadContext context, int argc, IRubyObject arg0,
 
     @JRubyMethod(name = "string=", required = 1)
     public IRubyObject set_string(ThreadContext context, IRubyObject arg) {
-        checkFrozen();
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1423,7 +1434,7 @@ public IRubyObject set_string(ThreadContext context, IRubyObject arg) {
 
     @JRubyMethod(name = "string")
     public IRubyObject string(ThreadContext context) {
-        RubyString string = getPtr().string;
+        RubyString string = getPtrForRead().string;
         if (string == null) return context.nil;
 
         return string;
@@ -1440,7 +1451,7 @@ public IRubyObject truncate(ThreadContext context, IRubyObject len) {
         checkWritable();
 
         int l = RubyFixnum.fix2int(len);
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
         RubyString string = ptr.string;
 
         boolean locked = lock(context, ptr);
@@ -1472,7 +1483,7 @@ public IRubyObject ungetc(ThreadContext context, IRubyObject arg) {
         checkModifiable();
         checkReadable();
 
-        if (getPtr().string == null) return context.nil;
+        if (getPtrForWrite().string == null) return context.nil;
 
         if (arg.isNil()) return arg;
         if (arg instanceof RubyInteger) {
@@ -1499,7 +1510,7 @@ public IRubyObject ungetc(ThreadContext context, IRubyObject arg) {
     }
 
     private void ungetbyteCommon(ThreadContext context, int c) {
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1530,7 +1541,7 @@ private void ungetbyteCommon(ThreadContext context, RubyString ungetBytes) {
     private void ungetbyteCommon(ThreadContext context, byte[] ungetBytes, int cp, int cl) {
         if (cl == 0) return;
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1585,7 +1596,7 @@ public IRubyObject ungetbyte(ThreadContext context, IRubyObject arg) {
         if (arg.isNil()) return arg;
 
         checkModifiable();
-        if (getPtr().string == null) return context.nil;
+        if (getPtrForWrite().string == null) return context.nil;
 
         if (arg instanceof RubyInteger) {
             ungetbyteCommon(context, ((RubyInteger) ((RubyInteger) arg).op_mod(context, 256)).getIntValue());
@@ -1699,7 +1710,7 @@ private long stringIOWrite(ThreadContext context, Ruby runtime, IRubyObject arg)
         RubyString str = arg.asString();
         int len, olen;
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1810,7 +1821,7 @@ public IRubyObject set_encoding(ThreadContext context, IRubyObject ext_enc) {
             }
         }
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -1846,7 +1857,7 @@ public IRubyObject set_encoding(ThreadContext context, IRubyObject enc, IRubyObj
 
     @JRubyMethod
     public IRubyObject set_encoding_by_bom(ThreadContext context) {
-        StringIOData ptr = getPtr();
+        StringIOData ptr = getPtrForWrite();
 
         if (setEncodingByBOM(context, ptr) == null) return context.nil;
 
@@ -1929,7 +1940,7 @@ public IRubyObject each_codepoint(ThreadContext context, Block block) {
 
         checkReadable();
 
-        StringIOData ptr = this.getPtr();
+        StringIOData ptr = this.getPtrForWrite();
 
         boolean locked = lock(context, ptr);
         try {
@@ -2179,17 +2190,17 @@ public IRubyObject puts(ThreadContext context, IRubyObject[] args) {
 
     private boolean readable() {
         return (flags & STRIO_READABLE) != 0
-                && (getPtr().flags & OpenFile.READABLE) != 0;
+                && (ptr.flags & OpenFile.READABLE) != 0;
     }
 
     private boolean writable() {
         return (flags & STRIO_WRITABLE) != 0
-                && (getPtr().flags & OpenFile.WRITABLE) != 0;
+                && (ptr.flags & OpenFile.WRITABLE) != 0;
     }
 
     private boolean closed() {
         return !((flags & STRIO_READWRITE) != 0
-                && (getPtr().flags & OpenFile.READWRITE) != 0);
+                && (ptr.flags & OpenFile.READWRITE) != 0);
     }
 
     /* rb: readable */
@@ -2211,7 +2222,7 @@ private void checkWritable() {
     }
 
     private void checkModifiable() {
-        final RubyString string = getPtr().string;
+        final RubyString string = getPtrForWrite().string;
         if (string == null) {
             /* Null device StringIO */
         } else if (string.isFrozen()) {
@@ -2222,7 +2233,7 @@ private void checkModifiable() {
     }
 
     private void checkInitialized() {
-        if (getPtr() == null) {
+        if (ptr == null) {
             throw getRuntime().newIOError("uninitialized stream");
         }
     }
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index c9d7a9f5..bde80b7f 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -62,6 +62,7 @@ struct StringIO {
     int count;
 };
 
+static struct StringIO *get_strio_for_read(VALUE self);
 static VALUE strio_init(int, VALUE *, struct StringIO *, VALUE);
 static VALUE strio_unget_bytes(struct StringIO *, const char *, long);
 static long strio_write(VALUE self, VALUE str);
@@ -126,8 +127,14 @@ static const rb_data_type_t strio_data_type = {
 static struct StringIO*
 get_strio(VALUE self)
 {
-    struct StringIO *ptr = check_strio(rb_io_taint_check(self));
+    rb_check_frozen(self);
+    return get_strio_for_read(self);
+}
 
+static struct StringIO*
+get_strio_for_read(VALUE self)
+{
+    struct StringIO *ptr = check_strio(self);
     if (!ptr) {
 	rb_raise(rb_eIOError, "uninitialized stream");
     }
@@ -155,6 +162,7 @@ strio_substr(struct StringIO *ptr, long pos, long len, rb_encoding *enc)
 }
 
 #define StringIO(obj) get_strio(obj)
+#define StringIOForRead(obj) get_strio_for_read(obj)
 
 #define STRIO_READABLE FL_USER4
 #define STRIO_WRITABLE FL_USER5
@@ -182,7 +190,7 @@ static VALUE sym_exception;
 static struct StringIO*
 readable(VALUE strio)
 {
-    struct StringIO *ptr = StringIO(strio);
+    struct StringIO *ptr = StringIOForRead(strio);
     if (!READABLE(strio)) {
 	rb_raise(rb_eIOError, "not opened for reading");
     }
@@ -387,7 +395,8 @@ strio_init(int argc, VALUE *argv, struct StringIO *ptr, VALUE self)
 static VALUE
 strio_finalize(VALUE self)
 {
-    struct StringIO *ptr = StringIO(self);
+    struct StringIO *ptr = check_strio(self);
+    if (!ptr) return Qnil;
     RB_OBJ_WRITE(self, &ptr->string, Qnil);
     ptr->flags &= ~FMODE_READWRITE;
     return self;
@@ -439,7 +448,7 @@ strio_s_new(int argc, VALUE *argv, VALUE klass)
 static VALUE
 strio_false(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     return Qfalse;
 }
 
@@ -449,7 +458,7 @@ strio_false(VALUE self)
 static VALUE
 strio_nil(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     return Qnil;
 }
 
@@ -459,7 +468,7 @@ strio_nil(VALUE self)
 static VALUE
 strio_self(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     return self;
 }
 
@@ -469,7 +478,7 @@ strio_self(VALUE self)
 static VALUE
 strio_0(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     return INT2FIX(0);
 }
 
@@ -479,7 +488,7 @@ strio_0(VALUE self)
 static VALUE
 strio_first(VALUE self, VALUE arg)
 {
-    StringIO(self);
+    StringIOForRead(self);
     return arg;
 }
 
@@ -489,7 +498,7 @@ strio_first(VALUE self, VALUE arg)
 static VALUE
 strio_unimpl(int argc, VALUE *argv, VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     rb_notimplement();
 
     UNREACHABLE;
@@ -517,7 +526,7 @@ strio_unimpl(int argc, VALUE *argv, VALUE self)
 static VALUE
 strio_get_string(VALUE self)
 {
-    return StringIO(self)->string;
+    return StringIOForRead(self)->string;
 }
 
 /*
@@ -650,7 +659,7 @@ strio_close_write(VALUE self)
 static VALUE
 strio_closed(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     if (!CLOSED(self)) return Qfalse;
     return Qtrue;
 }
@@ -671,7 +680,7 @@ strio_closed(VALUE self)
 static VALUE
 strio_closed_read(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     if (READABLE(self)) return Qfalse;
     return Qtrue;
 }
@@ -692,7 +701,7 @@ strio_closed_read(VALUE self)
 static VALUE
 strio_closed_write(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     if (WRITABLE(self)) return Qfalse;
     return Qtrue;
 }
@@ -738,7 +747,7 @@ strio_copy(VALUE copy, VALUE orig)
 
     orig = rb_convert_type(orig, T_DATA, "StringIO", "to_strio");
     if (copy == orig) return copy;
-    ptr = StringIO(orig);
+    ptr = StringIOForRead(orig);
     old_ptr = check_strio(copy);
     if (old_ptr) {
 	old_string = old_ptr->string;
@@ -762,7 +771,7 @@ strio_copy(VALUE copy, VALUE orig)
 static VALUE
 strio_get_lineno(VALUE self)
 {
-    return LONG2NUM(StringIO(self)->lineno);
+    return LONG2NUM(StringIOForRead(self)->lineno);
 }
 
 /*
@@ -850,7 +859,7 @@ strio_reopen(int argc, VALUE *argv, VALUE self)
 static VALUE
 strio_get_pos(VALUE self)
 {
-    return LONG2NUM(StringIO(self)->pos);
+    return LONG2NUM(StringIOForRead(self)->pos);
 }
 
 /*
@@ -942,7 +951,7 @@ strio_seek(int argc, VALUE *argv, VALUE self)
 static VALUE
 strio_get_sync(VALUE self)
 {
-    StringIO(self);
+    StringIOForRead(self);
     return Qtrue;
 }
 
@@ -1863,7 +1872,7 @@ strio_syswrite_nonblock(int argc, VALUE *argv, VALUE self)
 static VALUE
 strio_size(VALUE self)
 {
-    VALUE string = StringIO(self)->string;
+    VALUE string = StringIOForRead(self)->string;
     if (NIL_P(string)) {
 	return INT2FIX(0);
     }
@@ -1915,7 +1924,7 @@ strio_truncate(VALUE self, VALUE len)
 static VALUE
 strio_external_encoding(VALUE self)
 {
-    struct StringIO *ptr = StringIO(self);
+    struct StringIO *ptr = StringIOForRead(self);
     return rb_enc_from_encoding(get_enc(ptr));
 }
 
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index 02490626..656c0bb9 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -359,6 +359,9 @@ def test_open
 
   def test_isatty
     assert_equal(false, StringIO.new("").isatty)
+    assert_equal(false, StringIO.new("").tty?)
+    assert_nothing_raised { StringIO.new("").freeze.isatty}
+    assert_nothing_raised { StringIO.new("").freeze.tty?}
   end
 
   def test_fsync
@@ -368,6 +371,7 @@ def test_fsync
   def test_sync
     assert_equal(true, StringIO.new("").sync)
     assert_equal(false, StringIO.new("").sync = false)
+    assert_nothing_raised { StringIO.new("").freeze.sync}
   end
 
   def test_set_fcntl
@@ -420,8 +424,8 @@ def test_closed
     assert_equal(false, f.closed?)
     f.close
     assert_equal(true, f.closed?)
-  ensure
-    f.close unless f.closed?
+    f.freeze
+    assert_nothing_raised { f.closed? }
   end
 
   def test_closed_read
@@ -431,8 +435,8 @@ def test_closed_read
     assert_equal(false, f.closed_read?)
     f.close_read
     assert_equal(true, f.closed_read?)
-  ensure
-    f.close unless f.closed?
+    f.freeze
+    assert_nothing_raised { f.closed_read? }
   end
 
   def test_closed_write
@@ -442,8 +446,8 @@ def test_closed_write
     assert_equal(false, f.closed_write?)
     f.close_write
     assert_equal(true, f.closed_write?)
-  ensure
-    f.close unless f.closed?
+    f.freeze
+    assert_nothing_raised { f.closed_write? }
   end
 
   def test_dup
@@ -469,8 +473,8 @@ def test_lineno
     f.lineno = 1000
     assert_equal([1000, "baz\n"], [f.lineno, f.gets])
     assert_equal([1001, nil], [f.lineno, f.gets])
-  ensure
-    f.close unless f.closed?
+    f.freeze
+    assert_nothing_raised { f.lineno }
   end
 
   def test_pos
@@ -483,8 +487,8 @@ def test_pos
     assert_equal([4, "bar\n"], [f.pos, f.gets])
     assert_equal([8, "baz\n"], [f.pos, f.gets])
     assert_equal([12, nil], [f.pos, f.gets])
-  ensure
-    f.close unless f.closed?
+    f.freeze
+    assert_nothing_raised { f.pos }
   end
 
   def test_reopen
@@ -508,13 +512,10 @@ def test_seek
     assert_raise(Errno::EINVAL) { f.seek(1, 3) }
     f.close
     assert_raise(IOError) { f.seek(0) }
-  ensure
-    f.close unless f.closed?
-  end
-
-  def test_seek_frozen_string
     f = StringIO.new(-"1234")
     assert_equal(0, f.seek(1))
+  ensure
+    f.close unless f.closed?
   end
 
   def test_each_byte
@@ -837,11 +838,17 @@ def test_pread
     buf = "stale".b
     assert_equal "stale".b, StringIO.new("").pread(0, 0, buf)
     assert_equal "stale".b, buf
+
+    assert_nothing_raised { StringIO.new("pread").freeze.pread(3, 0)}
   end
 
   def test_size
     f = StringIO.new("1234")
     assert_equal(4, f.size)
+    assert_equal(4, f.length)
+    f.freeze
+    assert_nothing_raised { f.size }
+    assert_nothing_raised { f.length }
   end
 
   # This test is should in ruby/test_method.rb
@@ -1105,6 +1112,65 @@ def test_chilled_string_set_enocoding
     end
   end
 
+  def test_eof
+    f = StringIO.new
+    assert_equal(true, f.eof)
+    assert_equal(true, f.eof?)
+    f.ungetc("1234")
+    assert_equal(false, f.eof)
+    assert_equal(false, f.eof?)
+    f.freeze
+    assert_nothing_raised { f.eof }
+    assert_nothing_raised { f.eof? }
+  end
+
+  def test_pid
+    f = StringIO.new
+    assert_equal(nil, f.pid)
+    f.freeze
+    assert_nothing_raised { f.pid }
+  end
+
+  def test_fileno
+    f = StringIO.new
+    assert_equal(nil, f.fileno)
+    f.freeze
+    assert_nothing_raised { f.fileno }
+  end
+
+  def test_external_encoding
+    f = StringIO.new
+    assert_equal(Encoding.find("external"), f.external_encoding)
+    f = StringIO.new("1234".encode("UTF-16BE"))
+    assert_equal(Encoding::UTF_16BE, f.external_encoding)
+    f.freeze
+    assert_nothing_raised { f.external_encoding }
+  end
+
+  def test_string
+    f = StringIO.new
+    assert_equal("", f.string)
+    f = StringIO.new("1234")
+    assert_equal("1234", f.string)
+    f.freeze
+    assert_nothing_raised { f.string }
+  end
+
+  def test_initialize_copy
+    f = StringIO.new("1234")
+    f.read(1)
+    f2 = f.dup
+    assert_equal(1, f2.pos)
+    f.read(1)
+    assert_equal(2, f2.pos)
+    f.ungetc("56")
+    assert_equal(0, f2.pos)
+    assert_equal("5634", f2.string)
+    f.freeze
+    f2 = f.dup
+    assert_not_predicate(f2, :frozen?)
+  end
+
   private
 
   def assert_string(content, encoding, str, mesg = nil)