diff --git a/os/hal/lib/streams/chprintf.c b/os/hal/lib/streams/chprintf.c
index 4ecec7bcff..1d0398a55d 100644
--- a/os/hal/lib/streams/chprintf.c
+++ b/os/hal/lib/streams/chprintf.c
@@ -35,6 +35,7 @@
 #define MAX_FILLER 11
 #define FLOAT_PRECISION 9
 
+// returns pointer behind produced string
 static char *long_to_string_with_divisor(char *p,
                                          long num,
                                          unsigned radix,
@@ -79,9 +80,18 @@ static const long pow10[FLOAT_PRECISION] = {
     10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000
 };
 
-static char *ftoa(char *p, double num, unsigned long precision) {
+#define rusefi_cisnan(f) (*(((int*) (&f))) == 0x7FC00000)
+
+static char *ftoa(char *p, float num, unsigned long precision) {
   long l;
 
+  if (rusefi_cisnan(num)) {
+        *p ++ = 'N';
+        *p ++ = 'a';
+        *p ++ = 'N';
+        return p;
+  }
+
   if ((precision == 0) || (precision > FLOAT_PRECISION)) {
     precision = FLOAT_PRECISION;
   }
@@ -140,13 +150,13 @@ int chvprintf(BaseSequentialStream *chp, const char *fmt, va_list ap) {
     if (c == 0) {
       return n;
     }
-    
+
     if (c != '%') {
       streamPut(chp, (uint8_t)c);
       n++;
       continue;
     }
-    
+
     p = tmpbuf;
     s = tmpbuf;
 
@@ -170,7 +180,7 @@ int chvprintf(BaseSequentialStream *chp, const char *fmt, va_list ap) {
       fmt++;
       filler = '0';
     }
-    
+
     /* Width modifier.*/
     if ( *fmt == '*') {
       width = va_arg(ap, int);
@@ -193,7 +203,7 @@ int chvprintf(BaseSequentialStream *chp, const char *fmt, va_list ap) {
         }
       }
     }
-    
+
     /* Precision modifier.*/
     precision = 0;
     if (c == '.') {
@@ -216,7 +226,7 @@ int chvprintf(BaseSequentialStream *chp, const char *fmt, va_list ap) {
         }
       }
     }
-    
+
     /* Long modifier.*/
     if (c == 'l' || c == 'L') {
       is_long = true;