diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4462a79..b897a53 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -306,6 +306,7 @@ endif()
 check_type_size(time_t SIZEOF_TIME_T)
 if(SIZEOF_TIME_T STREQUAL "4")
 	set(SMALL_TIME_T true)
+	add_definitions(-DSMALL_TIME_T)
 	message(WARNING " ** Warning, this system is unable to represent times past 2038\n"
 	                " ** It will behave incorrectly when handling valid RFC5280 dates")
 endif()
diff --git a/configure.ac b/configure.ac
index 6f98b3e..384a2b6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -134,6 +134,7 @@ AC_CONFIG_FILES([
 
 AM_CONDITIONAL([SMALL_TIME_T], [test "$ac_cv_sizeof_time_t" = "4"])
 if test "$ac_cv_sizeof_time_t" = "4"; then
+    AC_DEFINE([SMALL_TIME_T])
     echo " ** Warning, this system is unable to represent times past 2038"
     echo " ** It will behave incorrectly when handling valid RFC5280 dates"