diff --git a/SFI.Tests/GraphTests.cs b/SFI.Tests/GraphTests.cs
index c705ab25..75bcd9f5 100644
--- a/SFI.Tests/GraphTests.cs
+++ b/SFI.Tests/GraphTests.cs
@@ -189,6 +189,11 @@ public async override ValueTask AddDefault()
                 {
                     mediaTypeAnalyzer.AddClasses = false;
                 }
+
+                if(Analyzers.OfType<ExtensionObjectAnalyzer>().FirstOrDefault() is ExtensionObjectAnalyzer extensionObjectAnalyzer)
+                {
+                    extensionObjectAnalyzer.AddClasses = false;
+                }
             }
         }
 
diff --git a/SFI/Analyzers/ExtensionObjectAnalyzer.cs b/SFI/Analyzers/ExtensionObjectAnalyzer.cs
index 76186396..d967de8b 100644
--- a/SFI/Analyzers/ExtensionObjectAnalyzer.cs
+++ b/SFI/Analyzers/ExtensionObjectAnalyzer.cs
@@ -10,6 +10,11 @@ namespace IS4.SFI.Analyzers
     /// </summary>
     public class ExtensionObjectAnalyzer : EntityAnalyzer<ExtensionObject>
     {
+        /// <summary>
+        /// Whether to add class information to the created node.
+        /// </summary>
+        public bool AddClasses { get; set; } = true;
+
         /// <inheritdoc cref="EntityAnalyzer.EntityAnalyzer"/>
         public ExtensionObjectAnalyzer()
         {
@@ -25,6 +30,10 @@ public async override ValueTask<AnalysisResult> Analyze(ExtensionObject extensio
                 node = context.NodeFactory.Create(Vocabularies.Uris, Uri.EscapeDataString(ext));
             }
             node = InitNewNode(node, context);
+            if(AddClasses)
+            {
+                node.SetClass(Classes.Extension);
+            }
             return new(node);
         }
     }
diff --git a/SFI/Vocabulary/Classes.cs b/SFI/Vocabulary/Classes.cs
index a48412a9..a56facf7 100644
--- a/SFI/Vocabulary/Classes.cs
+++ b/SFI/Vocabulary/Classes.cs
@@ -236,6 +236,12 @@ public static class Classes
         [Uri(Uriv, "Mimetype-Parametrized")]
         public static readonly ClassUri MediaTypeParametrized;
 
+        /// <summary>
+        /// <c><see cref="Uriv"/>:Suffix</c>.
+        /// </summary>
+        [Uri(Uriv, "Suffix")]
+        public static readonly ClassUri Extension;
+
         static Classes()
         {
             typeof(Classes).InitializeUris();