diff --git a/src/config.h.in b/src/config.h.in
index e63c51d716c056b60a1c77201dcd1a2fe41da218..56941870073aafda23c01405d21026201acb567a 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -82,3 +82,6 @@
 
 /* The size of a `off_t', as computed by sizeof. */
 #undef SIZEOF_OFF_T
+
+/* If zlib is available */
+#undef HAVE_LIBZ