diff --git a/ext/standard/incomplete_class.c b/ext/standard/incomplete_class.c
index 9863b8dc336..8294c69f965 100644
--- a/ext/standard/incomplete_class.c
+++ b/ext/standard/incomplete_class.c
@@ -42,8 +42,9 @@ static void incomplete_class_message(int error_type TSRMLS_DC)
 		class_name = php_lookup_class_name(EG(This), NULL);
 	}
 	
-	if (!class_name)
-		class_name = estrdup("unknown");
+	if (!class_name) {
+		class_name = estrndup("unknown", sizeof("unknown")-1);
+	}
 	
 	snprintf(buf, sizeof(buf)-1, INCOMPLETE_CLASS_MSG, class_name);