diff --git a/target-arm/op.c b/target-arm/op.c
index 5879eba..73f95b7 100644
--- a/target-arm/op.c
+++ b/target-arm/op.c
@@ -368,7 +368,7 @@
 void OPPROTO op_mull_T0_T1(void)
 {
     uint64_t res;
-    res = T0 * T1;
+    res = (uint64_t)T0 * (uint64_t)T1;
     T1 = res >> 32;
     T0 = res;
 }
@@ -377,7 +377,7 @@
 void OPPROTO op_imull_T0_T1(void)
 {
     uint64_t res;
-    res = (int32_t)T0 * (int32_t)T1;
+    res = (int64_t)T0 * (int64_t)T1;
     T1 = res >> 32;
     T0 = res;
 }