diff --git a/lib/parser.js b/lib/parser.js
index bad3970..498bdca 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -32,10 +32,39 @@ Parser.prototype.set = function (options) {
 
 
 Parser.prototype.render = function (src) {
-  var state;
+  var state, lineStart = 0, lastTabPos = 0;
 
   if (!src) { return ''; }
 
+  if (src.indexOf('\r') >= 0) {
+    src = src.replace(/\r/, '');
+  }
+
+  if (src.indexOf('\u00a0') >= 0) {
+    src = src.replace(/\u00a0/g, ' ');
+  }
+
+  if (src.indexOf('\u2424') >= 0) {
+    src = src.replace(/\u2424/g, '\n');
+  }
+
+  // TODO: benchmark it
+  // Replace tabs with proper number of spaces (1..4)
+  if (src.indexOf('\t') >= 0) {
+    src = src.replace(/[\n\t]/g, function (match, offset) {
+      var result;
+      if (src.charCodeAt(offset) === 0x0A) {
+        lineStart = offset + 1;
+        lastTabPos = 0;
+        return match;
+      }
+      result = '    '.slice((offset - lineStart - lastTabPos) % 4);
+      lastTabPos = offset - lineStart + 1;
+      return result;
+    });
+  }
+
+
   state = new State(
     src,
     this.lexerBlock,
diff --git a/lib/state.js b/lib/state.js
index 247d175..cf60342 100644
--- a/lib/state.js
+++ b/lib/state.js
@@ -15,11 +15,7 @@ function State(src, lexerBlock, lexerInline, renderer, tokens, options) {
   // - replace tabs with spaces
   // - remove `\r` to simplify newlines check (???)
 
-  this.src = src
-              .replace(/\t/g, '    ')
-              .replace(/\r/g, '')
-              .replace(/\u00a0/g, ' ')
-              .replace(/\u2424/g, '\n');
+  this.src = src;
 
   // Shortcuts to simplify nested calls
   this.lexerBlock  = lexerBlock;
diff --git a/test/fixtures/stmd/bad.txt b/test/fixtures/stmd/bad.txt
index 488ed3f..1cc5f9f 100644
--- a/test/fixtures/stmd/bad.txt
+++ b/test/fixtures/stmd/bad.txt
@@ -1,38 +1,3 @@
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-src line: 205
-
-.
-	foo	baz		bim
-.
-<pre><code>foo baz     bim
-</code></pre>
-.
-
-error:
-
-<pre><code>foo    baz        bim
-</code></pre>
-
-
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-src line: 212
-
-.
-    a	a
-    ὐ	a
-.
-<pre><code>a   a
-ὐ   a
-</code></pre>
-.
-
-error:
-
-<pre><code>a    a
-ὐ    a
-</code></pre>
-
-
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 src line: 395
 
@@ -1802,20 +1767,6 @@ error:
 <p>`hi`lo`</p>
 
 
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-src line: 3616
-
-.
-\	\A\a\ \3\φ\«
-.
-<p>\   \A\a\ \3\φ\«</p>
-.
-
-error:
-
-<p>\    \A\a\ \3\φ\«</p>
-
-
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 src line: 3647
 
diff --git a/test/fixtures/stmd/good.txt b/test/fixtures/stmd/good.txt
index 4d369fe..28f61d5 100644
--- a/test/fixtures/stmd/good.txt
+++ b/test/fixtures/stmd/good.txt
@@ -1,3 +1,25 @@
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+src line: 205
+
+.
+	foo	baz		bim
+.
+<pre><code>foo baz     bim
+</code></pre>
+.
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+src line: 212
+
+.
+    a	a
+    ὐ	a
+.
+<pre><code>a   a
+ὐ   a
+</code></pre>
+.
+
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 src line: 241
 
@@ -1741,6 +1763,15 @@ src line: 3607
 <p>!&quot;#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~</p>
 .
 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+src line: 3616
+
+.
+\	\A\a\ \3\φ\«
+.
+<p>\   \A\a\ \3\φ\«</p>
+.
+
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 src line: 3625