diff --git a/configure.ac b/configure.ac
index 8d3f308d7..079521fe5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -155,8 +155,8 @@ NEED_PROG(patch, patch)
 AC_PATH_PROG(xmllint, xmllint, false)
 AC_PATH_PROG(xsltproc, xsltproc, false)
 AC_PATH_PROG(w3m, w3m, false)
-AC_PATH_PROG(flex, flex, false)
-AC_PATH_PROG(bison, bison, false)
+NEED_PROG(flex, flex)
+NEED_PROG(bison, bison)
 NEED_PROG(perl, perl)
 NEED_PROG(sed, sed)
 NEED_PROG(tar, tar)