Index: ext/zlib/zlib.c
===================================================================
--- ext/zlib/zlib.c	(revision 22688)
+++ ext/zlib/zlib.c	(working copy)
@@ -695,7 +695,7 @@
 {
     uInt n;
     int err;
-    volatile VALUE guard;
+    volatile VALUE guard = Qnil;
 
     if (NIL_P(z->input) && len == 0) {
 	z->stream.next_in = (Bytef*)"";