diff --git a/ac/boost.m4 b/ac/boost.m4
index caaeeaa79..a45d9a8d9 100644
--- a/ac/boost.m4
+++ b/ac/boost.m4
@@ -1,2 +1,6 @@
 AX_BOOST_BASE()
 AX_BOOST_REGEX()
+
+if test x"$ax_cv_boost_regex" != "xyes"; then
+  AC_MSG_ERROR(The Boost regex library was not found.)
+fi