diff --git a/lib/VM/ArrayAccessDimension.php b/lib/VM/ArrayAccessDimension.php
index 3bc4a6e3d10..16811f113bb 100644
--- a/lib/VM/ArrayAccessDimension.php
+++ b/lib/VM/ArrayAccessDimension.php
@@ -24,6 +24,12 @@ public function __construct(\PHPCompiler\VM $vm, ObjectEntry $object, Variable $
         $this->callerFrame = $callerFrame;
     }
 
+    /**
+     * Live offsetGet payload (Zend read_dimension BP_VAR_RW).
+     *
+     * Assign-op ($obj[$k] += n) must use this value's runtime type, not the declared mixed
+     * return / TYPE_ARRAYACCESS_OFFSET view (#31947, zend_vm_def.h ZEND_ASSIGN_DIM_OP).
+     */
     public function read(): Variable
     {
         $out = new Variable();
@@ -37,7 +43,7 @@ public function read(): Variable
             throw new ArrayAccessOffsetSignal($catchFrame);
         }
 
-        return $out;
+        return $out->resolveIndirect();
     }
 
     public function write(Variable $value): void
diff --git a/lib/VM/Variable.php b/lib/VM/Variable.php
index 1ff1ab31762..05b8ac98864 100755
--- a/lib/VM/Variable.php
+++ b/lib/VM/Variable.php
@@ -1259,6 +1259,21 @@ public function readArrayAccessOffsetValue(): self
         return $this->arrayAccessDimension->read()->resolveIndirect();
     }
 
+    /**
+     * ZEND_ASSIGN_DIM_OP reads the live offsetGet payload, not the ArrayAccess view type (#31947).
+     *
+     * TYPE_ARRAYACCESS_OFFSET is named "mixed" in TypeErrors; assign-op must use the stored int/float.
+     */
+    private static function unwrapArrayAccessOperand(self $var): self
+    {
+        $var = $var->resolveIndirect();
+        if ($var->isArrayAccessOffset()) {
+            return $var->readArrayAccessOffsetValue();
+        }
+
+        return $var;
+    }
+
     public function arrayAccessOffsetClassName(): string
     {
         if (self::TYPE_ARRAYACCESS_OFFSET !== $this->type) {
@@ -2724,6 +2739,21 @@ public function bitwiseOp(
 
             return;
         }
+        if ($this->type === self::TYPE_ARRAYACCESS_OFFSET) {
+            $result = new self();
+            $result->bitwiseOp(
+                $opCode,
+                self::unwrapArrayAccessOperand($left),
+                self::unwrapArrayAccessOperand($right),
+                $vm,
+                $frame
+            );
+            $this->copyFrom($result);
+
+            return;
+        }
+        $left = self::unwrapArrayAccessOperand($left);
+        $right = self::unwrapArrayAccessOperand($right);
         $this->reset();
 restart:
         if ($left->type === self::TYPE_INDIRECT) {
@@ -2873,8 +2903,21 @@ public function numericOp(
 
             return;
         }
-        $left = $left->resolveIndirect();
-        $right = $right->resolveIndirect();
+        if ($this->type === self::TYPE_ARRAYACCESS_OFFSET) {
+            $result = new self();
+            $result->numericOp(
+                $opCode,
+                self::unwrapArrayAccessOperand($left),
+                self::unwrapArrayAccessOperand($right),
+                $vm,
+                $frame
+            );
+            $this->copyFrom($result);
+
+            return;
+        }
+        $left = self::unwrapArrayAccessOperand($left);
+        $right = self::unwrapArrayAccessOperand($right);
         TypedPropertyCheck::assertReadable($left);
         TypedPropertyCheck::assertReadable($right);
         if (OpCode::TYPE_PLUS === $opCode
@@ -2981,6 +3024,19 @@ public function incDecOp(
 
             return;
         }
+        if ($this->type === self::TYPE_ARRAYACCESS_OFFSET) {
+            $result = new self();
+            $result->incDecOp(
+                $opCode,
+                self::unwrapArrayAccessOperand($left),
+                self::unwrapArrayAccessOperand($right),
+                $vm,
+                $frame
+            );
+            $this->copyFrom($result);
+
+            return;
+        }
         if (self::TYPE_STRING_OFFSET === $this->type) {
             throw new \Error(self::STRING_OFFSET_INCDEC_ERROR);
         }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 4fca96b5f89..ee006f87c75 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -245,6 +245,8 @@
             <file>./test/compliance/ForeachByrefUninitTyped31836JITTest.php</file>
             <file>./test/compliance/ForeachByrefUnsetRefcount31936VMTest.php</file>
             <file>./test/compliance/ForeachByrefUnsetRefcount31936JITTest.php</file>
+            <file>./test/compliance/ArrayAccessAssignOp31947VMTest.php</file>
+            <file>./test/compliance/ArrayAccessAssignOp31947JITTest.php</file>
             <file>./test/compliance/ParentPrivateStaticArrayObjectProperty31937VMTest.php</file>
             <file>./test/compliance/VarExportArrayElementProperty31938VMTest.php</file>
             <file>./test/compliance/VarExportArrayElementProperty31938JITTest.php</file>
diff --git a/test/compliance/ArrayAccessAssignOp31947JITTest.php b/test/compliance/ArrayAccessAssignOp31947JITTest.php
new file mode 100644
index 00000000000..1c894ba1c32
--- /dev/null
+++ b/test/compliance/ArrayAccessAssignOp31947JITTest.php
@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+require_once __DIR__.'/../BaseTest.php';
+
+/**
+ * JIT: ArrayAccess by-ref offsetGet assign-op uses the live int (#31947).
+ *
+ * Dedicated provider — path-slash data-set names break --filter on full JITTest.
+ *
+ * @group llvm
+ */
+final class ArrayAccessAssignOp31947JITTest extends BaseTest
+{
+    protected static string $DIR = __DIR__;
+
+    public static function providePHPTests(): \Generator
+    {
+        yield 'arrayaccess_assign_op_byref.phpt' => self::parsePHPT(
+            __DIR__.'/cases/language/arrayaccess_assign_op_byref.phpt',
+            'arrayaccess_assign_op_byref.phpt'
+        );
+    }
+
+    public function setUp(): void
+    {
+        $this->BIN = realpath(__DIR__.'/../../bin/jit.php');
+    }
+}
diff --git a/test/compliance/ArrayAccessAssignOp31947VMTest.php b/test/compliance/ArrayAccessAssignOp31947VMTest.php
new file mode 100644
index 00000000000..d8927dfee7b
--- /dev/null
+++ b/test/compliance/ArrayAccessAssignOp31947VMTest.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+require_once __DIR__.'/../BaseTest.php';
+
+/**
+ * VM: ArrayAccess by-ref offsetGet assign-op uses the live int (#31947).
+ *
+ * Dedicated provider — path-slash data-set names break --filter on full VMTest.
+ */
+final class ArrayAccessAssignOp31947VMTest extends BaseTest
+{
+    protected static string $DIR = __DIR__;
+
+    public static function providePHPTests(): \Generator
+    {
+        yield 'arrayaccess_assign_op_byref.phpt' => self::parsePHPT(
+            __DIR__.'/cases/language/arrayaccess_assign_op_byref.phpt',
+            'arrayaccess_assign_op_byref.phpt'
+        );
+    }
+
+    public function setUp(): void
+    {
+        $this->BIN = realpath(__DIR__.'/../../bin/vm.php');
+    }
+}
diff --git a/test/compliance/cases/language/arrayaccess_assign_op_byref.phpt b/test/compliance/cases/language/arrayaccess_assign_op_byref.phpt
new file mode 100644
index 00000000000..fef9e320dda
--- /dev/null
+++ b/test/compliance/cases/language/arrayaccess_assign_op_byref.phpt
@@ -0,0 +1,49 @@
+--TEST--
+Language: ArrayAccess by-ref offsetGet assign-op writes live int (ZEND_ASSIGN_DIM_OP; #31947)
+--FILE--
+<?php
+class A implements ArrayAccess
+{
+    private $d = [0 => 1];
+
+    public function offsetExists(mixed $k): bool
+    {
+        return isset($this->d[$k]);
+    }
+
+    public function &offsetGet(mixed $k): mixed
+    {
+        return $this->d[$k];
+    }
+
+    public function offsetSet(mixed $k, mixed $v): void
+    {
+        $this->d[$k] = $v;
+    }
+
+    public function offsetUnset(mixed $k): void
+    {
+        unset($this->d[$k]);
+    }
+}
+
+$inc = new A();
+$inc[0]++;
+echo 'inc=', $inc[0], "\n";
+
+$plus = new A();
+$plus[0] += 2;
+echo 'plus=', $plus[0], "\n";
+
+$minus = new A();
+$minus[0] -= 1;
+echo 'minus=', $minus[0], "\n";
+
+$mul = new A();
+$mul[0] *= 3;
+echo 'mul=', $mul[0], "\n";
+--EXPECT--
+inc=2
+plus=3
+minus=0
+mul=3