diff --git a/parallel_hashmap/phmap_bits.h b/parallel_hashmap/phmap_bits.h
index 7eb3fac..1d9c413 100644
--- a/parallel_hashmap/phmap_bits.h
+++ b/parallel_hashmap/phmap_bits.h
@@ -337,10 +337,17 @@ PHMAP_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
 #endif
 
 #ifdef PHMAP_HAVE_INTRINSIC_INT128
+
+    #if defined(__GNUC__) && !defined(__clang__)
+        #define PHMAP_EXTENSION 
+    #else
+        #define PHMAP_EXTENSION __extension__
+    #endif
+
     inline uint64_t umul128(uint64_t a, uint64_t b, uint64_t* high) 
     {
-        auto result = static_cast<__extension__ unsigned __int128>(a) * 
-                      static_cast<__extension__ unsigned __int128>(b);
+        auto result = static_cast<PHMAP_EXTENSION unsigned __int128>(a) * 
+                      static_cast<PHMAP_EXTENSION unsigned __int128>(b);
         *high = static_cast<uint64_t>(result >> 64);
         return static_cast<uint64_t>(result);
     }