diff --git a/error.c b/error.c
index e78071c686..6e0fb7dfe3 100644
--- a/error.c
+++ b/error.c
@@ -1072,7 +1072,7 @@ die(void)
 }
 
 RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, 1, 0)
-void
+static void
 rb_bug_without_die(const char *fmt, va_list args)
 {
     const char *file = NULL;