diff --git a/src/atomicops_internals_x86_gcc.cc b/src/atomicops_internals_x86_gcc.cc
index 950b423f41..a119cd2ab2 100644
--- a/src/atomicops_internals_x86_gcc.cc
+++ b/src/atomicops_internals_x86_gcc.cc
@@ -77,10 +77,10 @@ namespace {
 void AtomicOps_Internalx86CPUFeaturesInit() {
   using v8::internal::AtomicOps_Internalx86CPUFeatures;
 
-  uint32_t eax;
-  uint32_t ebx;
-  uint32_t ecx;
-  uint32_t edx;
+  uint32_t eax = 0;
+  uint32_t ebx = 0;
+  uint32_t ecx = 0;
+  uint32_t edx = 0;
 
   // Get vendor string (issue CPUID with eax = 0)
   cpuid(eax, ebx, ecx, edx, 0);
diff --git a/src/platform-posix.cc b/src/platform-posix.cc
index 5ca12522c1..20c25338be 100644
--- a/src/platform-posix.cc
+++ b/src/platform-posix.cc
@@ -213,6 +213,11 @@ void* OS::GetRandomMmapAddr() {
   // smarter about using mmap address hints.
   // See http://code.google.com/p/nativeclient/issues/3341
   return NULL;
+#endif
+#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
+    defined(THREAD_SANITIZER)
+  // Dynamic tools do not support custom mmap addresses.
+  return NULL;
 #endif
   Isolate* isolate = Isolate::UncheckedCurrent();
   // Note that the current isolate isn't set up in a call path via
diff --git a/src/v8utils.h b/src/v8utils.h
index 058b153a7e..32c5c2e5d3 100644
--- a/src/v8utils.h
+++ b/src/v8utils.h
@@ -215,6 +215,11 @@ inline void MemsetPointer(T** dest, U* value, int counter) {
 #undef STOS
 #endif
 
+#if defined(MEMORY_SANITIZER)
+  // MemorySanitizer does not understand inline assembly.
+#undef STOS
+#endif
+
 #if defined(__GNUC__) && defined(STOS)
   asm volatile(
       "cld;"