diff --git a/vnc-encoding-zlib.c b/vnc-encoding-zlib.c
index 6a16a799479f5f7f5d2cc31b23598e7a1344a1ed..29dd1b7aee7bc627e038e5a8c085f62bb82d05da 100644
--- a/vnc-encoding-zlib.c
+++ b/vnc-encoding-zlib.c
@@ -83,10 +83,17 @@ static int vnc_zlib_stop(VncState *vs)
             return -1;
         }
 
+        vs->zlib_level = vs->tight_compression;
         zstream->opaque = vs;
     }
 
-    // XXX what to do if tight_compression changed in between?
+    if (vs->tight_compression != vs->zlib_level) {
+        if (deflateParams(zstream, vs->tight_compression,
+                          Z_DEFAULT_STRATEGY) != Z_OK) {
+            return -1;
+        }
+        vs->zlib_level = vs->tight_compression;
+    }
 
     // reserve memory in output buffer
     buffer_reserve(&vs->output, vs->zlib.offset + 64);
diff --git a/vnc.h b/vnc.h
index 6d92c60b12d50e31a5232bcf5e60315449d0bd05..380068794320e3708c745c4e23767a087b33b8f1 100644
--- a/vnc.h
+++ b/vnc.h
@@ -178,6 +178,7 @@ struct VncState
     Buffer zlib;
     Buffer zlib_tmp;
     z_stream zlib_stream;
+    int zlib_level;
 
     Notifier mouse_mode_notifier;