diff --git a/src/System.Management.Automation/engine/CommandCompletion/ExtensibleCompletion.cs b/src/System.Management.Automation/engine/CommandCompletion/ExtensibleCompletion.cs
index 6905e39b165..53fe6f7b5e2 100644
--- a/src/System.Management.Automation/engine/CommandCompletion/ExtensibleCompletion.cs
+++ b/src/System.Management.Automation/engine/CommandCompletion/ExtensibleCompletion.cs
@@ -58,6 +58,7 @@ public ArgumentCompleterAttribute(ScriptBlock scriptBlock)
     /// <summary>
     /// A type specified by the <see cref="ArgumentCompleterAttribute"/> must implement this interface.
     /// </summary>
+#nullable enable
     public interface IArgumentCompleter
     {
         /// <summary>
@@ -82,6 +83,7 @@ IEnumerable<CompletionResult> CompleteArgument(
             CommandAst commandAst,
             IDictionary fakeBoundParameters);
     }
+#nullable restore
 
     /// <summary>
     /// </summary>