diff --git a/include/proto/compression.h b/include/proto/compression.h
index 1614edd..0eaa216 100644
--- a/include/proto/compression.h
+++ b/include/proto/compression.h
@@ -41,6 +41,8 @@
 
 
 #ifdef USE_ZLIB
+extern long zlib_used_memory;
+
 int deflate_init(struct comp_ctx **comp_ctx, int level);
 int deflate_add_data(struct comp_ctx *comp_ctx, const char *in_data, int in_len, struct buffer *out);
 int deflate_flush(struct comp_ctx *comp_ctx, struct buffer *out, int flag);