Raise an ArgumentError for unknown pack/unpack directive

* [Bug #19150]

1 files changed, 1 insertions, 1 deletions

diff --git a/pack.c b/pack.c
index 3bdae01362..f1f474759a 100644
--- a/pack.c
+++ b/pack.c
@@ -167,7 +167,7 @@ unknown_directive(const char *mode, char type, VALUE fmt)
         snprintf(unknown, sizeof(unknown), "\\x%.2x", type & 0xff);
     }
     fmt = rb_str_quote_unprintable(fmt);
-    rb_warn("unknown %s directive '%s' in '%"PRIsVALUE"'",
+    rb_raise(rb_eArgError, "unknown %s directive '%s' in '%"PRIsVALUE"'",
             mode, unknown, fmt);
 }