diff --git a/common/rdr/Exception.cxx b/common/rdr/Exception.cxx
index d70cd9f..964bc33 100644
--- a/common/rdr/Exception.cxx
+++ b/common/rdr/Exception.cxx
@@ -50,7 +50,7 @@
 }
 
 SystemException::SystemException(const char* s, int err_)
-  : Exception(s), err(err_)
+  : Exception("%s", s), err(err_)
 {
   strncat(str_, ": ", len-1-strlen(str_));
 #ifdef _WIN32