diff --git a/cf/krb-prog-yacc.m4 b/cf/krb-prog-yacc.m4
index 6abe48e3c..1764e38da 100644
--- a/cf/krb-prog-yacc.m4
+++ b/cf/krb-prog-yacc.m4
@@ -5,4 +5,8 @@ dnl We prefer byacc or yacc because they do not use `alloca'
 dnl
 
 AC_DEFUN(AC_KRB_PROG_YACC,
-[AC_CHECK_PROGS(YACC, byacc yacc 'bison -y')])
+[AC_CHECK_PROGS(YACC, byacc yacc 'bison -y')
+if test "$YACC" = ""; then
+  AC_MSG_WARNING([yacc not found - some stuff will not build])
+fi
+])