diff --git a/relaxng.c b/relaxng.c
index 345f354..56a3344 100644
--- a/relaxng.c
+++ b/relaxng.c
@@ -2215,7 +2215,8 @@
         snprintf(msg, 1000, "Unknown error code %d\n", err);
     }
     msg[1000 - 1] = 0;
-    return (xmlStrdup((xmlChar *) msg));
+    xmlChar *result = xmlCharStrdup(msg);
+    return (xmlEscapeFormatString(&result));
 }
 
 /**