diff --git a/sprintf.c b/sprintf.c
index 8a4662b..f93c542 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -126,7 +126,7 @@ sign_bits(int base, const char *p)
     (rb_raise(rb_eArgError, "named%.*s after unnumbered(%d)", (len), (name), posarg), 0) : \
     posarg == -1 ? \
     (rb_raise(rb_eArgError, "named%.*s after numbered", (len), (name)), 0) :	\
-    (posarg = -2, rb_hash_lookup2(get_hash(&hash, argc, argv), id, Qundef)))
+    (posarg = -2, rb_hash_aref(get_hash(&hash, argc, argv), id)))
 
 #define GETNUM(n, val) \
     for (; p < end && rb_enc_isdigit(*p, enc); p++) {	\