diff --git a/lib/deflate.js b/lib/deflate.js
index 7ce5cf5..2e29d62 100644
--- a/lib/deflate.js
+++ b/lib/deflate.js
@@ -95,7 +95,7 @@ Deflate.prototype.push = function(data, mode) {
 
   if (this.ended) { return false; }
 
-  _mode = (mode === true) ? c.Z_FINISH : (isNaN(mode) ? c.Z_NO_FLUSH : mode);
+  _mode = (mode === ~~mode) ? mode : ((mode === true) ? c.Z_FINISH : c.Z_NO_FLUSH);
 
   strm.next_in = data;
   strm.next_in_index = 0;