diff --git a/common/rfb/KeyRemapper.cxx b/common/rfb/KeyRemapper.cxx
index 05f0763..d33f0a4 100644
--- a/common/rfb/KeyRemapper.cxx
+++ b/common/rfb/KeyRemapper.cxx
@@ -50,7 +50,7 @@
       if (bidi == '<')
         mapping[to] = from;
     } else {
-      vlog.error("warning: bad mapping %.*s", nextComma-m, m);
+      vlog.error("warning: bad mapping %.*s", (int)(nextComma-m), m);
     }
     m = nextComma;
     if (nextComma[0])