diff --git a/.gitignore b/.gitignore
index 8681871..e1cfe81 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 /doc
 /node_modules/
+/coverage
+
diff --git a/.jshintignore b/.jshintignore
index 6264b72..265b534 100644
--- a/.jshintignore
+++ b/.jshintignore
@@ -1,3 +1,4 @@
 .git/
 node_modules/
 benchmark/implementations
+coverage/
diff --git a/.npmignore b/.npmignore
index 35ac5e1..9804234 100644
--- a/.npmignore
+++ b/.npmignore
@@ -1,5 +1,6 @@
-/banchmark/
+/benchmark/
 /test/
+/coverage/
 /.*
 /Makefile
 
diff --git a/Makefile b/Makefile
index 3a92167..8c91cc5 100644
--- a/Makefile
+++ b/Makefile
@@ -35,6 +35,9 @@ test: lint
 		fi
 	mocha
 
+cover:
+	rm -rf cover
+	istanbul cover node_modules/.bin/_mocha -- -t 30000 -R spec
 
 doc:
 	@if test ! `which ndoc` ; then \
diff --git a/lib/deflate.js b/lib/deflate.js
index 96db340..b4196aa 100644
--- a/lib/deflate.js
+++ b/lib/deflate.js
@@ -93,7 +93,7 @@ function sliceBuf(buf, size) {
 var Deflate = function(options) {
 
   this.options = utils.assign({
-    level: 6,
+    level: c.Z_DEFAULT_COMPRESSION,
     method: c.Z_DEFLATED,
     chunkSize: 16384,
     windowBits: 15,
diff --git a/lib/zlib/deflate.js b/lib/zlib/deflate.js
index 28f30c1..9dc9a5f 100644
--- a/lib/zlib/deflate.js
+++ b/lib/zlib/deflate.js
@@ -1206,14 +1206,16 @@ function DeflateState() {
 }
 
 function deflateResetKeep(strm) {
-  strm.total_in = strm.total_out = 0;
-  strm.data_type = c.Z_UNKNOWN;
+  var s;
 
   if (!strm || !strm.state) {
     return c.Z_STREAM_ERROR;
   }
 
-  var s = strm.state;
+  strm.total_in = strm.total_out = 0;
+  strm.data_type = c.Z_UNKNOWN;
+
+  s = strm.state;
   s.pending = 0;
   s.pending_out = 0;
 
diff --git a/lib/zlib/zstream.js b/lib/zlib/zstream.js
index 32252ce..2b5f7ee 100644
--- a/lib/zlib/zstream.js
+++ b/lib/zlib/zstream.js
@@ -19,7 +19,7 @@ function ZStream() {
   /* not visible by applications */
   this.state = null;
   /* best guess about the data type: binary or text */
-  this.data_type = 2;
+  this.data_type = 2/*Z_UNKNOWN*/;
   /* adler32 value of the uncompressed data */
   this.adler = 0;
 }
diff --git a/test/deflate.js b/test/deflate.js
index 73817b1..f4b7a2b 100644
--- a/test/deflate.js
+++ b/test/deflate.js
@@ -64,7 +64,9 @@ describe('Deflate levels', function () {
   it('level 0', function(done) {
     testDeflate(zlib.createDeflate, pako.deflate, samples, { level: 0 }, done);
   });
-
+  it('level -1 (implicit default)', function(done) {
+    testDeflate(zlib.createDeflate, pako.deflate, samples, { level: 0 }, done);
+  });
 });
 
 
@@ -94,6 +96,9 @@ describe('Deflate windowBits', function () {
   it('windowBits 8', function(done) {
     testDeflate(zlib.createDeflate, pako.deflate, samples, { windowBits: 8 }, done);
   });
+  it('windowBits -15 (implicit raw)', function(done) {
+    testDeflate(zlib.createDeflateRaw, pako.deflate, samples, { windowBits: -15 }, done);
+  });
 
 });
 
diff --git a/test/helpers.js b/test/helpers.js
index 87bf4e0..177dbfb 100644
--- a/test/helpers.js
+++ b/test/helpers.js
@@ -54,7 +54,12 @@ function cmpBuf(a, b) {
 //
 function testDeflateSingle(zlib_factory, pako_deflate, data, options, callback) {
 
-  var zlibStream = zlib_factory(options);
+  var zlib_options = _.clone(options);
+
+  // hack for testing negative windowBits
+  if (zlib_options.windowBits < 0) { zlib_options.windowBits = -zlib_options.windowBits; }
+
+  var zlibStream = zlib_factory(zlib_options);
   var buffers = [], nread = 0;