diff --git a/src/Buffertools/Parser.php b/src/Buffertools/Parser.php
index 1565bbe..5ca477c 100644
--- a/src/Buffertools/Parser.php
+++ b/src/Buffertools/Parser.php
@@ -26,25 +26,19 @@ class Parser
     /**
      * Instantiate class, optionally taking Buffer or HEX.
      *
-     * @param null|string|BufferInterface $input
+     * @param BufferInterface $input
      */
-    public function __construct($input = null)
+    public function __construct(BufferInterface $input = null)
     {
-        if (null === $input) {
-            $input = '';
-        }
+        $this->position = 0;
 
-        if (is_string($input)) {
-            $bin = Buffer::hex($input, null)->getBinary();
-        } elseif ($input instanceof BufferInterface) {
-            $bin = $input->getBinary();
+        if (null === $input) {
+            $this->string = '';
+            $this->size = 0;
         } else {
-            throw new \InvalidArgumentException("Invalid argument to Parser");
+            $this->string = $input->getBinary();
+            $this->size = $input->getSize();
         }
-
-        $this->string = $bin;
-        $this->position = 0;
-        $this->size = strlen($this->string);
     }
 
     /**
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index e2dbc36..46757b0 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -39,20 +39,20 @@ public function testGetBufferEmptyNull()
 
     public function testWriteBytes()
     {
-        $bytes = '41424344';
+        $bytes = Buffer::hex('41424344');
+
         $parser = new Parser();
-        $parser->writeBytes(4, Buffer::hex($bytes));
-        $returned = $parser->getBuffer()->getHex();
-        $this->assertSame($returned, '41424344');
+        $parser->writeBytes(4, $bytes);
+        $this->assertTrue($parser->getBuffer()->equals($bytes));
     }
 
     public function testWriteBytesFlip()
     {
-        $bytes = '41424344';
+        $bytes = Buffer::hex('41424344');
         $parser = new Parser();
-        $parser->writeBytes(4, Buffer::hex($bytes), true);
-        $returned = $parser->getBuffer()->getHex();
-        $this->assertSame($returned, '44434241');
+        $parser->writeBytes(4, $bytes, true);
+
+        $this->assertEquals('44434241', $parser->getBuffer()->getHex());
     }
 
     public function testWriteBytesPadded()
@@ -71,26 +71,24 @@ public function testWriteBytesFlipPadded()
 
     public function testReadBytes()
     {
-        $bytes = '41424344';
+        $bytes = Buffer::hex('41424344');
 
         $parser = new Parser($bytes);
         $read = $parser->readBytes(4);
         $this->assertInstanceOf(Buffer::class, $read);
 
-        $hex = $read->getHex();
-        $this->assertSame($bytes, $hex);
+        $this->assertTrue($read->equals($bytes));
     }
 
     public function testReadBytesFlip()
     {
-        $bytes = '41424344';
+        $bytes = Buffer::hex('41424344');
 
         $parser = new Parser($bytes);
         $read = $parser->readBytes(4, true);
         $this->assertInstanceOf(Buffer::class, $read);
 
-        $hex = $read->getHex();
-        $this->assertSame('44434241', $hex);
+        $this->assertEquals($bytes->flip()->getHex(), $read->getHex());
     }
 
     /**
@@ -103,8 +101,7 @@ public function testReadBytesEmpty()
         // and length is zero.
 
         $parser = new Parser();
-        $data = $parser->readBytes(0);
-        $this->assertFalse(!!$data);
+        $parser->readBytes(0);
     }
     /**
      * @expectedException \BitWasp\Buffertools\Exceptions\ParserOutOfRange
@@ -112,7 +109,7 @@ public function testReadBytesEmpty()
      */
     public function testReadBytesEndOfString()
     {
-        $parser = new Parser('4041414142414141');
+        $parser = new Parser(Buffer::hex('4041414142414141'));
         $bytes1 = $parser->readBytes(4);
         $bytes2 = $parser->readBytes(4);
         $this->assertSame($bytes1->getHex(), '40414141');
@@ -125,7 +122,7 @@ public function testReadBytesEndOfString()
      */
     public function testReadBytesBeyondLength()
     {
-        $bytes = '41424344';
+        $bytes = Buffer::hex('41424344');
         $parser = new Parser($bytes);
         $parser->readBytes(5);
     }
diff --git a/tests/TemplateTest.php b/tests/TemplateTest.php
index 84f8c19..f42b409 100644
--- a/tests/TemplateTest.php
+++ b/tests/TemplateTest.php
@@ -29,7 +29,7 @@ public function testTemplate()
     public function testTemplateEmptyParse()
     {
         $template = new Template();
-        $parser = new Parser('010203040a0b0c0d');
+        $parser = new Parser(Buffer::hex('010203040a0b0c0d'));
         $template->parse($parser);
     }