diff --git a/builtin-log.c b/builtin-log.c
index dcc9f81793..9458428a8b 100644
--- a/builtin-log.c
+++ b/builtin-log.c
@@ -219,7 +219,7 @@ static int git_log_config(const char *var, const char *value)
 {
 	if (!strcmp(var, "format.subjectprefix")) {
 		if (!value)
-			die("format.subjectprefix without value");
+			config_error_nonbool(var);
 		fmt_patch_subject_prefix = xstrdup(value);
 		return 0;
 	}