diff --git a/src/Markdig.Tests/Specs/DefinitionListSpecs.generated.cs b/src/Markdig.Tests/Specs/DefinitionListSpecs.generated.cs
index b76cf50..2a707fe 100644
--- a/src/Markdig.Tests/Specs/DefinitionListSpecs.generated.cs
+++ b/src/Markdig.Tests/Specs/DefinitionListSpecs.generated.cs
@@ -101,7 +101,7 @@ namespace Markdig.Tests.Specs.DefinitionLists
             TestParser.TestSpec("Term 1\n\n:   Definition\nwith lazy continuation.\n\n    Second paragraph of the definition.", "<dl>\n<dt>Term 1</dt>\n<dd><p>Definition\nwith lazy continuation.</p>\n<p>Second paragraph of the definition.</p>\n</dd>\n</dl>", "definitionlists+attributes|advanced", context: "Example 2\nSection Extensions / Definition lists\n");
         }
 
-        // The definition must be indented to 4 characters including the `:`. 
+        // The `:` or `~` must be followed by at least one space or tab. A single space is enough:
         [Test]
         public void ExtensionsDefinitionLists_Example003()
         {
@@ -109,17 +109,26 @@ namespace Markdig.Tests.Specs.DefinitionLists
             // Section: Extensions / Definition lists
             //
             // The following Markdown:
-            //     Term 1
-            //     :  Invalid with less than 3 characters
+            //     First Term
+            //     : This is the definition of the first term.
+            //     
+            //     Second Term
+            //     : This is one definition of the second term.
+            //     ~ This is another definition of the second term.
             //
             // Should be rendered as:
-            //     <p>Term 1
-            //     :  Invalid with less than 3 characters</p>
+            //     <dl>
+            //     <dt>First Term</dt>
+            //     <dd>This is the definition of the first term.</dd>
+            //     <dt>Second Term</dt>
+            //     <dd>This is one definition of the second term.</dd>
+            //     <dd>This is another definition of the second term.</dd>
+            //     </dl>
 
-            TestParser.TestSpec("Term 1\n:  Invalid with less than 3 characters", "<p>Term 1\n:  Invalid with less than 3 characters</p>", "definitionlists+attributes|advanced", context: "Example 3\nSection Extensions / Definition lists\n");
+            TestParser.TestSpec("First Term\n: This is the definition of the first term.\n\nSecond Term\n: This is one definition of the second term.\n~ This is another definition of the second term.", "<dl>\n<dt>First Term</dt>\n<dd>This is the definition of the first term.</dd>\n<dt>Second Term</dt>\n<dd>This is one definition of the second term.</dd>\n<dd>This is another definition of the second term.</dd>\n</dl>", "definitionlists+attributes|advanced", context: "Example 3\nSection Extensions / Definition lists\n");
         }
 
-        // The `:` can be indented up to 3 spaces:
+        // Without a space or tab after the `:`, the line is not a definition:
         [Test]
         public void ExtensionsDefinitionLists_Example004()
         {
@@ -128,6 +137,24 @@ namespace Markdig.Tests.Specs.DefinitionLists
             //
             // The following Markdown:
             //     Term 1
+            //     :Invalid without a space after the colon
+            //
+            // Should be rendered as:
+            //     <p>Term 1
+            //     :Invalid without a space after the colon</p>
+
+            TestParser.TestSpec("Term 1\n:Invalid without a space after the colon", "<p>Term 1\n:Invalid without a space after the colon</p>", "definitionlists+attributes|advanced", context: "Example 4\nSection Extensions / Definition lists\n");
+        }
+
+        // The `:` can be indented up to 3 spaces:
+        [Test]
+        public void ExtensionsDefinitionLists_Example005()
+        {
+            // Example 5
+            // Section: Extensions / Definition lists
+            //
+            // The following Markdown:
+            //     Term 1
             //        : Valid even if `:` starts at most 3 spaces
             //
             // Should be rendered as:
@@ -136,14 +163,14 @@ namespace Markdig.Tests.Specs.DefinitionLists
             //     <dd>Valid even if <code>:</code> starts at most 3 spaces</dd>
             //     </dl>
 
-            TestParser.TestSpec("Term 1\n   : Valid even if `:` starts at most 3 spaces", "<dl>\n<dt>Term 1</dt>\n<dd>Valid even if <code>:</code> starts at most 3 spaces</dd>\n</dl>", "definitionlists+attributes|advanced", context: "Example 4\nSection Extensions / Definition lists\n");
+            TestParser.TestSpec("Term 1\n   : Valid even if `:` starts at most 3 spaces", "<dl>\n<dt>Term 1</dt>\n<dd>Valid even if <code>:</code> starts at most 3 spaces</dd>\n</dl>", "definitionlists+attributes|advanced", context: "Example 5\nSection Extensions / Definition lists\n");
         }
 
         // But more than 3 spaces before `:` will trigger an indented code block:
         [Test]
-        public void ExtensionsDefinitionLists_Example005()
+        public void ExtensionsDefinitionLists_Example006()
         {
-            // Example 5
+            // Example 6
             // Section: Extensions / Definition lists
             //
             // The following Markdown:
@@ -156,14 +183,14 @@ namespace Markdig.Tests.Specs.DefinitionLists
             //     <pre><code>: Not valid
             //     </code></pre>
 
-            TestParser.TestSpec("Term 1\n\n    : Not valid", "<p>Term 1</p>\n<pre><code>: Not valid\n</code></pre>", "definitionlists+attributes|advanced", context: "Example 5\nSection Extensions / Definition lists\n");
+            TestParser.TestSpec("Term 1\n\n    : Not valid", "<p>Term 1</p>\n<pre><code>: Not valid\n</code></pre>", "definitionlists+attributes|advanced", context: "Example 6\nSection Extensions / Definition lists\n");
         }
 
         // Definition lists can be nested inside list items
         [Test]
-        public void ExtensionsDefinitionLists_Example006()
+        public void ExtensionsDefinitionLists_Example007()
         {
-            // Example 6
+            // Example 7
             // Section: Extensions / Definition lists
             //
             // The following Markdown:
@@ -189,7 +216,7 @@ namespace Markdig.Tests.Specs.DefinitionLists
             //     </dl></li>
             //     </ol>
 
-            TestParser.TestSpec("1.  First\n    \n2.  Second\n    \n    Term 1\n    :   Definition\n    \n    Term 2\n    :   Second Definition", "<ol>\n<li><p>First</p></li>\n<li><p>Second</p>\n<dl>\n<dt>Term 1</dt>\n<dd>Definition</dd>\n<dt>Term 2</dt>\n<dd>Second Definition</dd>\n</dl></li>\n</ol>", "definitionlists+attributes|advanced", context: "Example 6\nSection Extensions / Definition lists\n");
+            TestParser.TestSpec("1.  First\n    \n2.  Second\n    \n    Term 1\n    :   Definition\n    \n    Term 2\n    :   Second Definition", "<ol>\n<li><p>First</p></li>\n<li><p>Second</p>\n<dl>\n<dt>Term 1</dt>\n<dd>Definition</dd>\n<dt>Term 2</dt>\n<dd>Second Definition</dd>\n</dl></li>\n</ol>", "definitionlists+attributes|advanced", context: "Example 7\nSection Extensions / Definition lists\n");
         }
     }
 }
diff --git a/src/Markdig.Tests/Specs/DefinitionListSpecs.md b/src/Markdig.Tests/Specs/DefinitionListSpecs.md
index b0b1522..aaf9163 100644
--- a/src/Markdig.Tests/Specs/DefinitionListSpecs.md
+++ b/src/Markdig.Tests/Specs/DefinitionListSpecs.md
@@ -72,14 +72,33 @@ with lazy continuation.</p>
 </dl>
 ````````````````````````````````
 
-The definition must be indented to 4 characters including the `:`. 
+The `:` or `~` must be followed by at least one space or tab. A single space is enough:
+
+```````````````````````````````` example
+First Term
+: This is the definition of the first term.
+
+Second Term
+: This is one definition of the second term.
+~ This is another definition of the second term.
+.
+<dl>
+<dt>First Term</dt>
+<dd>This is the definition of the first term.</dd>
+<dt>Second Term</dt>
+<dd>This is one definition of the second term.</dd>
+<dd>This is another definition of the second term.</dd>
+</dl>
+````````````````````````````````
+
+Without a space or tab after the `:`, the line is not a definition:
 
 ```````````````````````````````` example
 Term 1
-:  Invalid with less than 3 characters
+:Invalid without a space after the colon
 .
 <p>Term 1
-:  Invalid with less than 3 characters</p>
+:Invalid without a space after the colon</p>
 ````````````````````````````````
 
 The `:` can be indented up to 3 spaces:
diff --git a/src/Markdig/Extensions/DefinitionLists/DefinitionListParser.cs b/src/Markdig/Extensions/DefinitionLists/DefinitionListParser.cs
index 85eb808..191fbc1 100644
--- a/src/Markdig/Extensions/DefinitionLists/DefinitionListParser.cs
+++ b/src/Markdig/Extensions/DefinitionLists/DefinitionListParser.cs
@@ -2,6 +2,7 @@
 // This file is licensed under the BSD-Clause 2 license. 
 // See the license.txt file in the project root for more information.
 
+using Markdig.Helpers;
 using Markdig.Parsers;
 using Markdig.Syntax;
 
@@ -35,12 +36,12 @@ public class DefinitionListParser : BlockParser
         var startPosition = processor.Start;
 
         var column = processor.ColumnBeforeIndent;
-        processor.NextChar();
+        var c = processor.NextChar();
         processor.ParseIndent();
         var delta = processor.Column - column;
 
-        // We expect to have a least
-        if (delta < 4)
+        // The marker must be followed by at least one space or tab
+        if (!c.IsSpaceOrTab())
         {
             // Return back to original position
             processor.GoToColumn(column);
@@ -144,12 +145,12 @@ public class DefinitionListParser : BlockParser
         {
             var startPosition = processor.Start;
             var column = processor.ColumnBeforeIndent;
-            processor.NextChar();
+            var c = processor.NextChar();
             processor.ParseIndent();
             var delta = processor.Column - column;
 
-            // We expect to have a least
-            if (delta < 4)
+            // The marker must be followed by at least one space or tab
+            if (!c.IsSpaceOrTab())
             {
                 // Remove the blankline before breaking this definition item
                 if (lastBlankLine != null)