diff --git a/lib/zlib/deflate.js b/lib/zlib/deflate.js
index 9761d0d..b7b4188 100644
--- a/lib/zlib/deflate.js
+++ b/lib/zlib/deflate.js
@@ -1306,7 +1306,7 @@ function deflateSetHeader(strm, head) {
 
 function deflateInit2(strm, level, method, windowBits, memLevel, strategy) {
   if (!strm) { // === Z_NULL
-    return err(strm, Z_STREAM_ERROR);
+    return Z_STREAM_ERROR;
   }
   var wrap = 1;
 
@@ -1386,7 +1386,7 @@ function deflate(strm, flush) {
 
   if (!strm || !strm.state ||
     flush > Z_BLOCK || flush < 0) {
-    return err(strm, Z_STREAM_ERROR);
+    return strm ? err(strm, Z_STREAM_ERROR) : Z_STREAM_ERROR;
   }
 
   s = strm.state;
diff --git a/test/deflate_cover.js b/test/deflate_cover.js
new file mode 100644
index 0000000..2dc51d3
--- /dev/null
+++ b/test/deflate_cover.js
@@ -0,0 +1,96 @@
+// Deflate coverage tests
+
+/*global describe, it*/
+
+
+'use strict';
+
+
+var assert = require('assert');
+var fs = require('fs');
+var path  = require('path');
+
+var c = require('../lib/zlib/constants');
+var msg = require('../lib/zlib/messages');
+var zlib_deflate = require('../lib/zlib/deflate.js');
+var zstream = require('../lib/zlib/zstream');
+
+var pako  = require('../index');
+
+
+var short_sample = 'hello world';
+var long_sample = fs.readFileSync(path.join(__dirname, 'fixtures/samples/lorem_en_100k.txt'));
+
+function testDeflate(data, opts, flush) {
+  var deflator = new pako.Deflate(opts);
+  deflator.push(data, flush);
+  deflator.push(data, true);
+
+  assert.equal(deflator.err, false, msg[deflator.err]);
+}
+
+describe('Deflate support', function() {
+  it('stored', function() {
+    testDeflate(short_sample, {level: 0, chunkSize: 200}, 0);
+    testDeflate(short_sample, {level: 0, chunkSize: 10}, 5);
+  });
+  it('fast', function() {
+    testDeflate(short_sample, {level: 1, chunkSize: 10}, 5);
+    testDeflate(long_sample, {level: 1, memLevel: 1, chunkSize: 10}, 0);
+  });
+  it('slow', function() {
+    testDeflate(short_sample, {level: 4, chunkSize: 10}, 5);
+    testDeflate(long_sample, {level: 9, memLevel: 1, chunkSize: 10}, 0);
+  });
+  it('rle', function() {
+    testDeflate(short_sample, {strategy: 3}, 0);
+    testDeflate(short_sample, {strategy: 3, chunkSize: 10}, 5);
+    testDeflate(long_sample, {strategy: 3, chunkSize: 10}, 0);
+  });
+  it('huffman', function() {
+    testDeflate(short_sample, {strategy: 2}, 0);
+    testDeflate(short_sample, {strategy: 2, chunkSize: 10}, 5);
+    testDeflate(long_sample, {strategy: 2, chunkSize: 10}, 0);
+
+  });
+});
+
+describe('Deflate states', function() {
+  //in port checking input parameters was removed
+  it('inflate bad parameters', function () {
+    var ret, strm;
+
+    ret = zlib_deflate.deflate(null, 0);
+    assert(ret === c.Z_STREAM_ERROR);
+
+    strm = new zstream();
+
+    ret = zlib_deflate.deflateInit(null);
+    assert(ret === c.Z_STREAM_ERROR);
+
+    ret = zlib_deflate.deflateInit(strm, 6);
+    assert(ret === c.Z_OK);
+
+    ret = zlib_deflate.deflateSetHeader(null);
+    assert(ret === c.Z_STREAM_ERROR);
+
+    strm.state.wrap = 1;
+    ret = zlib_deflate.deflateSetHeader(strm, null);
+    assert(ret === c.Z_STREAM_ERROR);
+
+    strm.state.wrap = 2;
+    ret = zlib_deflate.deflateSetHeader(strm, null);
+    assert(ret === c.Z_OK);
+
+    ret = zlib_deflate.deflate(strm, c.Z_FINISH);
+    assert(ret === c.Z_BUF_ERROR);
+
+    ret = zlib_deflate.deflateEnd(null);
+    assert(ret === c.Z_STREAM_ERROR);
+
+    //BS_NEED_MORE
+    strm.state.status = 5;
+    ret = zlib_deflate.deflateEnd(strm);
+    assert(ret === c.Z_STREAM_ERROR);
+  });
+});
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