diff --git a/system/include/emscripten/xmmintrin.h b/system/include/emscripten/xmmintrin.h
index 4868c8221df86..ceb9acc1cc486 100644
--- a/system/include/emscripten/xmmintrin.h
+++ b/system/include/emscripten/xmmintrin.h
@@ -120,6 +120,12 @@ _mm_store_ps(float *__p, __m128 __a)
 // No NTA cache hint available.
 #define _mm_stream_ps _mm_store_ps
 
+static __inline__ void __attribute__((__always_inline__))
+_mm_sfence(void)
+{
+  __sync_synchronize(); // Emscripten/SharedArrayBuffer has only a full barrier instruction, which gives a stronger guarantee.
+}
+
 #define _MM_SHUFFLE(w, z, y, x) (((w) << 6) | ((z) << 4) | ((y) << 2) | (x))
 
 // This is defined as a macro because __builtin_shufflevector requires its
diff --git a/tests/test_sse1.cpp b/tests/test_sse1.cpp
index 87680279bc0d7..e155c52176312 100644
--- a/tests/test_sse1.cpp
+++ b/tests/test_sse1.cpp
@@ -332,8 +332,8 @@ int main()
 	_mm_prefetch(dummyData, _MM_HINT_T1);
 	_mm_prefetch(dummyData, _MM_HINT_T2);
 	_mm_prefetch(dummyData, _MM_HINT_NTA);
-	_mm_sfence();
 #endif
+	_mm_sfence();
 
 	// SSE1 Misc instructions:
 #ifdef TEST_M64