diff --git a/src/lib/subs/fortdef.c b/src/lib/subs/fortdef.c
index 29579937..23b78504 100644
--- a/src/lib/subs/fortdef.c
+++ b/src/lib/subs/fortdef.c
@@ -144,7 +144,7 @@ sd(natid att, natid own, coord x, coord y, int noisy, int defending,
 	    }
 	}
     }
-    return (int)100 - eff * 100;
+    return (int)(100 - eff * 100);
 }
 
 int