diff --git a/src/reduce.c b/src/reduce.c
index 9f9c2ee7..b440516e 100644
--- a/src/reduce.c
+++ b/src/reduce.c
@@ -93,7 +93,7 @@ unsigned i;
   int count = 0;
 
   while (i != 0) {
-    i ^= (i & -i);
+    i ^= (i & ((unsigned) (- (int) i)));
     ++count;
   }
   return count;