diff --git a/configure.ac b/configure.ac
index 5bdddfab..396b5ef3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -164,7 +164,7 @@ elif test "x${ac_cv_sizeof_intmax_t}" = "x8" ; then
 elif test "x${ac_cv_sizeof_intmax_t}" = "x4" ; then
   LG_SIZEOF_INTMAX_T=2
 else
-  AC_MSG_ERROR([Unsupported intmax_t size: ${ac_cv_sizeof_long}])
+  AC_MSG_ERROR([Unsupported intmax_t size: ${ac_cv_sizeof_intmax_t}])
 fi
 AC_DEFINE_UNQUOTED([LG_SIZEOF_INTMAX_T], [$LG_SIZEOF_INTMAX_T])