diff --git a/src/arith_uint256.h b/src/arith_uint256.h
--- a/src/arith_uint256.h
+++ b/src/arith_uint256.h
@@ -69,7 +69,7 @@
         base_uint ret;
         for (int i = 0; i < WIDTH; i++)
             ret.pn[i] = ~pn[i];
-        ret++;
+        ++ret;
         return ret;
     }