diff --git a/mult/imult64.c b/mult/imult64.c
index ecf4f30..231ca55 100644
--- a/mult/imult64.c
+++ b/mult/imult64.c
@@ -22,6 +22,16 @@ void imult64() {
 
 #include "safemult.h"
 
+#if defined(__GNUC__) && (defined(__x86_64__) || defined(__ia64__) || defined(__powerpc64__) || defined(__alpha__) || defined(__mips64__) || defined(__sparc64__))
+
+int imult64(int64 a,int64 b,int64* c) {
+  __int128_t x=((__int128_t)a)*b;
+  if ((*c=(int64)x) != x) return 0;
+  return 1;
+}
+
+#else
+
 int imult64(int64 a,int64 b,int64* c) {
   int neg=(a<0);
   uint64 d;
@@ -34,3 +44,5 @@ int imult64(int64 a,int64 b,int64* c) {
 }
 
 #endif
+
+#endif
diff --git a/mult/umult64.c b/mult/umult64.c
index d4ecf2c..db72ee2 100644
--- a/mult/umult64.c
+++ b/mult/umult64.c
@@ -21,7 +21,7 @@ void umult64() {
 
 #include "safemult.h"
 
-#ifdef __GNUC__
+#if defined(__GNUC__) && (defined(__x86_64__) || defined(__ia64__) || defined(__powerpc64__) || defined(__alpha__) || defined(__mips64__) || defined(__sparc64__))
 
 int umult64(uint64 a,uint64 b,uint64* c) {
   __uint128_t x=((__uint128_t)a)*b;