diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 910d7600a9..4585fa70ce 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -1305,9 +1305,19 @@ void Assembler::leal(Register dst, const Operand& src) {
 
 void Assembler::load_rax(void* value, RelocInfo::Mode mode) {
   EnsureSpace ensure_space(this);
-  emit(0x48);  // REX.W
-  emit(0xA1);
-  emitp(value, mode);
+  if (kPointerSize == kInt64Size) {
+    emit(0x48);  // REX.W
+    emit(0xA1);
+    emitp(value, mode);
+  } else {
+    ASSERT(kPointerSize == kInt32Size);
+    emit(0xA1);
+    emitp(value, mode);
+    // In 64-bit mode, need to zero extend the operand to 8 bytes.
+    // See 2.2.1.4 in Intel64 and IA32 Architectures Software
+    // Developer's Manual Volume 2.
+    emitl(0);
+  }
 }
 
 
@@ -1888,9 +1898,19 @@ void Assembler::xchgl(Register dst, Register src) {
 
 void Assembler::store_rax(void* dst, RelocInfo::Mode mode) {
   EnsureSpace ensure_space(this);
-  emit(0x48);  // REX.W
-  emit(0xA3);
-  emitp(dst, mode);
+  if (kPointerSize == kInt64Size) {
+    emit(0x48);  // REX.W
+    emit(0xA3);
+    emitp(dst, mode);
+  } else {
+    ASSERT(kPointerSize == kInt32Size);
+    emit(0xA3);
+    emitp(dst, mode);
+    // In 64-bit mode, need to zero extend the operand to 8 bytes.
+    // See 2.2.1.4 in Intel64 and IA32 Architectures Software
+    // Developer's Manual Volume 2.
+    emitl(0);
+  }
 }