diff --git a/include/rapidjson/internal/biginteger.h b/include/rapidjson/internal/biginteger.h
index af48738..4930043 100644
--- a/include/rapidjson/internal/biginteger.h
+++ b/include/rapidjson/internal/biginteger.h
@@ -259,7 +259,7 @@ private:
         if (low < k)
             (*outHigh)++;
         return low;
-#elif (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) && defined(__x86_64__)
+#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) && defined(__x86_64__)
         __extension__ typedef unsigned __int128 uint128;
         uint128 p = static_cast<uint128>(a) * static_cast<uint128>(b);
         p += k;
diff --git a/include/rapidjson/internal/diyfp.h b/include/rapidjson/internal/diyfp.h
index f7d4653..1f60fb6 100644
--- a/include/rapidjson/internal/diyfp.h
+++ b/include/rapidjson/internal/diyfp.h
@@ -79,7 +79,7 @@ struct DiyFp {
         if (l & (uint64_t(1) << 63)) // rounding
             h++;
         return DiyFp(h, e + rhs.e + 64);
-#elif (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) && defined(__x86_64__)
+#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) && defined(__x86_64__)
         __extension__ typedef unsigned __int128 uint128;
         uint128 p = static_cast<uint128>(f) * static_cast<uint128>(rhs.f);
         uint64_t h = static_cast<uint64_t>(p >> 64);