diff --git a/configure.ac b/configure.ac
index 204a745..472cc14 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,6 +16,24 @@ AC_PROG_CC_C99
 AC_C_CONST
 AC_PROG_LIBTOOL
 
+# backwards compat with older pkg-config
+# - pull in AC_DEFUN from pkg.m4
+m4_ifndef([PKG_CHECK_VAR], [
+# PKG_CHECK_VAR(VARIABLE, MODULE, CONFIG-VARIABLE,
+# [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
+# -------------------------------------------
+# Retrieves the value of the pkg-config variable for the given module.
+AC_DEFUN([PKG_CHECK_VAR],
+[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
+AC_ARG_VAR([$1], [value of $3 for $2, overriding pkg-config])dnl
+
+_PKG_CONFIG([$1], [variable="][$3]["], [$2])
+AS_VAR_COPY([$1], [pkg_cv_][$1])
+
+AS_VAR_IF([$1], [""], [$5], [$4])dnl
+])# PKG_CHECK_VAR
+])
+
 case $host_os in
         *linux*)
                 linux=yes