diff --git a/lib/inflate.js b/lib/inflate.js
index 4b9fa08..358cc33 100644
--- a/lib/inflate.js
+++ b/lib/inflate.js
@@ -10,11 +10,6 @@ var zstream = require('./zlib/zstream');
 var gzheader = require('./zlib/gzheader');
 
 
-// calculate tail size of utf8 char by current byte value
-function utf8tail(code) {
-  return code >= 252 ? 6 : code >= 248 ? 5 : code >= 240 ? 4 : code >= 224 ? 3 : code >= 192 ? 2 : 1;
-}
-
 /**
  * class Inflate
  *
@@ -220,10 +215,10 @@ Inflate.prototype.push = function(data, mode) {
           next_out_utf8_index = strm.next_out_index - 6;
           if (next_out_utf8_index < 0) { next_out_utf8_index = 0; }
 
-          tail = utf8tail(strm.next_out[next_out_utf8_index]);
+          tail = strings.utf8tail(strm.next_out[next_out_utf8_index]);
           while (next_out_utf8_index + tail <= strm.next_out_index) {
             next_out_utf8_index += tail;
-            tail = utf8tail(strm.next_out[next_out_utf8_index]);
+            tail = strings.utf8tail(strm.next_out[next_out_utf8_index]);
           }
 
           // shit happened - broken tail. then take it all.
diff --git a/lib/utils/strings.js b/lib/utils/strings.js
index fe317b5..b1a8363 100644
--- a/lib/utils/strings.js
+++ b/lib/utils/strings.js
@@ -119,3 +119,9 @@ exports.binstring2buf = function(str) {
   }
   return buf;
 };
+
+
+// calculate tail size of utf8 char by current byte value
+exports.utf8tail = function(code) {
+  return code >= 252 ? 6 : code >= 248 ? 5 : code >= 240 ? 4 : code >= 224 ? 3 : code >= 192 ? 2 : 1;
+};