diff --git a/lib/zlib/adler32.js b/lib/zlib/adler32.js
index 299d10a..cb93380 100644
--- a/lib/zlib/adler32.js
+++ b/lib/zlib/adler32.js
@@ -5,24 +5,27 @@
 // Small size is preferable.
 
 function adler32(adler, buf, len, pos) {
-  var s1 = adler & 0xffff
-    , s2 = (adler >>> 16) & 0xffff
+  var s1 = (adler & 0xffff) |0
+    , s2 = ((adler >>> 16) & 0xffff) |0
     , n = 0;
 
   while (len !== 0) {
-    n = len > 5552 ? 5552 : len;
+    // Set limit ~ twice less than 5552, to keep
+    // s2 in 31-bits, because we force signed ints.
+    // in other case %= will fail.
+    n = len > 2000 ? 2000 : len;
     len -= n;
 
     do {
-      s1 += buf[pos++];
-      s2 += s1;
+      s1 = (s1 + buf[pos++]) |0;
+      s2 = (s2 + s1) |0;
     } while (--n);
 
     s1 %= 65521;
     s2 %= 65521;
   }
 
-  return (s1 | (s2 << 16));
+  return (s1 | (s2 << 16)) |0;
 }