diff --git a/opal/util/os_path.c b/opal/util/os_path.c
index 5a29e9767c..8eb54f43f7 100644
--- a/opal/util/os_path.c
+++ b/opal/util/os_path.c
@@ -59,7 +59,7 @@ char *opal_os_path(int relative, ...)
     	if (relative) {
             path[0] = '.';
         }
-        strncat(path, path_sep, len);
+        strncat(path, path_sep, len - 1);
     	return(path);
     }