diff --git a/CommonMark.Tests/GeneralTests.cs b/CommonMark.Tests/GeneralTests.cs
index 4cdcd77..f441cc1 100644
--- a/CommonMark.Tests/GeneralTests.cs
+++ b/CommonMark.Tests/GeneralTests.cs
@@ -17,7 +17,7 @@ public class GeneralTests
         [TestCategory("Security")]
         public void TestZeroCharRemoval()
         {
-            Helpers.ExecuteTest("\u0000*foo*\0", "<p><em>foo</em></p>");
+            Helpers.ExecuteTest("\u0000*foo*\0", "<p>\uFFFD<em>foo</em>\uFFFD</p>");
         }
 
         [TestMethod]
diff --git a/CommonMark.Tests/SourcePositionTests.cs b/CommonMark.Tests/SourcePositionTests.cs
index 1c02e5f..c386400 100644
--- a/CommonMark.Tests/SourcePositionTests.cs
+++ b/CommonMark.Tests/SourcePositionTests.cs
@@ -165,7 +165,7 @@ public void SourcePositionComplex()
             {
                 "**foo**",
                 "foo",
-                "bar",
+                "\0bar",
                 "*quoting **is nice***",
                 "**is nice**",
                 "`right`",
diff --git a/CommonMark/Parser/TabTextReader.cs b/CommonMark/Parser/TabTextReader.cs
index 705a8d6..80523df 100644
--- a/CommonMark/Parser/TabTextReader.cs
+++ b/CommonMark/Parser/TabTextReader.cs
@@ -80,17 +80,7 @@ public void ReadLine(LineInfo line)
                     }
                     else if (c == '\0')
                     {
-                        if (!useBuilder)
-                        {
-                            useBuilder = true;
-                            this._builder.Length = 0;
-                        }
-
-                        if (line.IsTrackingPositions)
-                            line.AddOffset(this._previousBufferLength + num + tabIncreaseCount, 1);
-
-                        this._builder.Append(this._buffer, this._bufferPosition, num - this._bufferPosition);
-                        this._bufferPosition = num + 1;
+                        this._buffer[num] = '\uFFFD';
                     }
 
                     num++;