diff --git a/builtin/config.c b/builtin/config.c
index 97b58c4aea..752d0c65d7 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -595,7 +595,7 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 	int nongit = !startup_info->have_repository;
 	char *value;
 
-	given_config_source.file = getenv(CONFIG_ENVIRONMENT);
+	given_config_source.file = xstrdup_or_null(getenv(CONFIG_ENVIRONMENT));
 
 	argc = parse_options(argc, argv, prefix, builtin_config_options,
 			     builtin_config_usage,