diff --git a/simd-support/sse2.c b/simd-support/sse2.c
--- a/simd-support/sse2.c
+++ b/simd-support/sse2.c
@@ -52,6 +52,11 @@
 
   static int sse2_works(void)
   {
+#ifdef __native_client__
+       /* NaCl doesn't support signal() to test whether SSE2 works, so we
+        * just trust cpuid when it says that SSE2 is supported */
+       return 1;
+#else
        void (*oldsig)(int);
        oldsig = signal(SIGILL, sighandler);
        if (setjmp(jb)) {
@@ -68,6 +73,7 @@
 	    signal(SIGILL, oldsig);
 	    return 1;
        }
+#endif
   }
 
   extern void X(check_alignment_of_sse2_pm)(void);
diff --git a/simd-support/x86-cpuid.h b/simd-support/x86-cpuid.h
--- a/simd-support/x86-cpuid.h
+++ b/simd-support/x86-cpuid.h
@@ -29,6 +29,13 @@
 
 static inline int is_386() 
 {
+#ifdef __native_client__
+  /* NaCl is not supported on 386 or any system that does not have the cpuid
+   instruction. Furthermore, pushf/popf are illegal instructions. So we
+   short-circuit these functions, returning false for is_386 and true for
+   has_cpuid */
+  return 0;
+#else
 #ifdef _MSC_VER
     unsigned int result,tst;
     _asm {
@@ -63,10 +70,14 @@ static inline int is_386()
     );
 #endif
     return (result == tst);
+#endif
 }
 
 static inline int has_cpuid() 
 {
+#ifdef __native_client__
+    return 1;
+#else
 #ifdef _MSC_VER
     unsigned int result,tst;
     _asm {
@@ -101,6 +112,7 @@ static inline int has_cpuid()
     );
 #endif
     return (result != tst);
+#endif
 }
 
 static inline int cpuid_edx(int op)
diff --git a/threads/threads.c b/threads/threads.c
--- a/threads/threads.c
+++ b/threads/threads.c
@@ -137,7 +137,11 @@ static void os_create_thread(FFTW_WORKER (*worker)(void *arg),
      pthread_t tid;
 
      pthread_attr_init(&attr);
+#if !defined(__native_client__) || defined(__GLIBC__)
+     // NaCl newlib doesn't define PTHREAD_SCOPE_SYSTEM.
+     // See https://code.google.com/p/nativeclient/issues/detail?id=3721
      pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM); 
+#endif
      pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
 
      pthread_create(&tid, &attr, worker, (void *)arg);