diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 572c36c881..3a657bd541 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -255,6 +255,7 @@ OS::MemCopyFunction CreateMemCopyFunction() {
   ASSERT(desc.reloc_size == 0);
 
   CPU::FlushICache(buffer, actual_size);
+  OS::ProtectCode(buffer, actual_size);
   return FUNCTION_CAST<OS::MemCopyFunction>(buffer);
 }
 
diff --git a/src/platform-posix.cc b/src/platform-posix.cc
index deb4b75618..1ea53c83ea 100644
--- a/src/platform-posix.cc
+++ b/src/platform-posix.cc
@@ -70,6 +70,12 @@ intptr_t OS::MaxVirtualMemory() {
 }
 
 
+// Get rid of writable permission on code allocations.
+void OS::ProtectCode(void* address, const size_t size) {
+  mprotect(address, size, PROT_READ | PROT_EXEC);
+}
+
+
 // Create guard pages.
 void OS::Guard(void* address, const size_t size) {
   mprotect(address, size, PROT_NONE);
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index b23e25ec97..e5df5ff3bf 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -957,6 +957,12 @@ void OS::Free(void* address, const size_t size) {
 }
 
 
+void OS::ProtectCode(void* address, const size_t size) {
+  DWORD old_protect;
+  VirtualProtect(address, size, PAGE_EXECUTE_READ, &old_protect);
+}
+
+
 void OS::Guard(void* address, const size_t size) {
   DWORD oldprotect;
   VirtualProtect(address, size, PAGE_READONLY | PAGE_GUARD, &oldprotect);
diff --git a/src/platform.h b/src/platform.h
index 4d7f9cf775..6b2348c890 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -207,6 +207,9 @@ class OS {
                         bool is_executable);
   static void Free(void* address, const size_t size);
 
+  // Mark code segments non-writable.
+  static void ProtectCode(void* address, const size_t size);
+
   // Assign memory as a guard page so that access will cause an exception.
   static void Guard(void* address, const size_t size);
 
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index f8f2d6e687..507bbd44c3 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -132,6 +132,7 @@ ModuloFunction CreateModuloFunction() {
 
   CodeDesc desc;
   masm.GetCode(&desc);
+  OS::ProtectCode(buffer, actual_size);
   // Call the function from C++ through this pointer.
   return FUNCTION_CAST<ModuloFunction>(buffer);
 }