diff --git a/src/Markdig.Tests/TestPlayParser.cs b/src/Markdig.Tests/TestPlayParser.cs
index 3d90a300..53420b1d 100644
--- a/src/Markdig.Tests/TestPlayParser.cs
+++ b/src/Markdig.Tests/TestPlayParser.cs
@@ -9,6 +9,13 @@ namespace Markdig.Tests;
 [TestFixture]
 public class TestPlayParser
 {
+
+    [Test]
+    public void TestInvalidSetext()
+    {
+        TestParser.TestSpec("test\n===n", "<p>test\n===n</p>", "advanced");
+    }
+
     [Test]
     public void TestBugWithEmphasisAndTable()
     {
diff --git a/src/Markdig/Parsers/ParagraphBlockParser.cs b/src/Markdig/Parsers/ParagraphBlockParser.cs
index 9e45715d..467a81b4 100644
--- a/src/Markdig/Parsers/ParagraphBlockParser.cs
+++ b/src/Markdig/Parsers/ParagraphBlockParser.cs
@@ -171,13 +171,9 @@ private static char GetHeadingChar(ref StringSlice line, ref int count)
         {
             count = line.CountAndSkipChar(headingChar);
 
-            if (line.IsEmpty)
-            {
-                return headingChar;
-            }
-
-            while (line.NextChar().IsSpaceOrTab())
+            while (line.CurrentChar.IsSpaceOrTab())
             {
+                line.NextChar();
             }
 
             if (line.IsEmpty)