diff --git a/config.h.cmake.in b/config.h.cmake.in
index fef3649..54f6035 100644
--- a/config.h.cmake.in
+++ b/config.h.cmake.in
@@ -1,3 +1,4 @@
+#cmakedefine HAVE_SOCKLEN_T
 #cmakedefine HAVE_INET_ATON
 #cmakedefine HAVE_INET_NTOP
 #cmakedefine HAVE_SNPRINTF