diff --git a/src/Markdig/Extensions/CustomContainers/CustomContainerExtension.cs b/src/Markdig/Extensions/CustomContainers/CustomContainerExtension.cs
index d07d4a4c..1a38013e 100644
--- a/src/Markdig/Extensions/CustomContainers/CustomContainerExtension.cs
+++ b/src/Markdig/Extensions/CustomContainers/CustomContainerExtension.cs
@@ -30,7 +30,11 @@ public void Setup(MarkdownPipelineBuilder pipeline)
             {
                 if (delimiterCount == 2 && emphasisChar == ':')
                 {
-                    return new CustomContainerInline();
+                    return new CustomContainerInline
+                    {
+                        DelimiterChar = ':',
+                        DelimiterCount = 2
+                    };
                 }
                 return null;
             });