diff --git a/configure.ac b/configure.ac
index 457c7e1cee307e29415ca1bf343824928b2452c7..8a9ad02944bf249748b4489046d6ea5b4be43c26 100644
--- a/configure.ac
+++ b/configure.ac
@@ -9,6 +9,8 @@ AC_ARG_WITH([compiler],[Haskell compiler])
 
 AC_PROG_CC()
 
+AC_USE_SYSTEM_EXTENSIONS
+
 AC_CONFIG_HEADERS([lib/include/HsTimeConfig.h])
 
 AC_CHECK_HEADERS([time.h])