diff --git a/src/instructions_portable.cpp b/src/instructions_portable.cpp
index d7467271..5d5921fe 100644
--- a/src/instructions_portable.cpp
+++ b/src/instructions_portable.cpp
@@ -123,10 +123,10 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef HAVE_SMULH
 	int64_t smulh(int64_t a, int64_t b) {
-		int64_t hi = mulh(a, b);
+		uint64_t hi = mulh(a, b);
 		if (a < 0LL) hi -= b;
 		if (b < 0LL) hi -= a;
-		return hi;
+		return unsigned64ToSigned2sCompl(hi);
 	}
 	#define HAVE_SMULH
 #endif