diff --git a/src/common/xstring.c b/src/common/xstring.c
index 96efcb3a6590ef7eb80d0eb24880facbf0e28618..d72eeb1831b7216466f6fd2e8260799113176455 100644
--- a/src/common/xstring.c
+++ b/src/common/xstring.c
@@ -68,6 +68,9 @@ static void makespace(char **str, int needed)
  */
 void _xstrcat(char **str1, const char *str2)
 {
+	if (str2 == NULL) 
+		str2 = "(null)";
+
 	makespace(str1, strlen(str2));
 	strcat(*str1, str2);
 }