diff --git a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs
index 1080421986cd..c2f2bfa321ca 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs
@@ -93,7 +93,7 @@ protected void PopulateType(TextWriter trapFile)
 
             // Visit base types
             var baseTypes = new List<Type>();
-            if (symbol.BaseType != null)
+            if (symbol.BaseType != null && symbol.BaseType.SpecialType != SpecialType.System_Object)
             {
                 Type baseKey = Create(Context, symbol.BaseType);
                 trapFile.extend(this, baseKey.TypeRef);
@@ -101,11 +101,6 @@ protected void PopulateType(TextWriter trapFile)
                     baseTypes.Add(baseKey);
             }
 
-            if (symbol.TypeKind == TypeKind.Interface)
-            {
-                trapFile.extend(this, Create(Context, Context.Compilation.ObjectType));
-            }
-
             if (!(base.symbol is IArrayTypeSymbol))
             {
                 foreach (var t in base.symbol.Interfaces.Select(i=>Create(Context, i)))
diff --git a/csharp/ql/src/semmle/code/csharp/Type.qll b/csharp/ql/src/semmle/code/csharp/Type.qll
index 0536098cf4a7..af62a994ac38 100644
--- a/csharp/ql/src/semmle/code/csharp/Type.qll
+++ b/csharp/ql/src/semmle/code/csharp/Type.qll
@@ -111,7 +111,13 @@ class ValueOrRefType extends DotNet::ValueOrRefType, Type, Attributable, @value_
   }
 
   /** Gets the immediate base class of this class, if any. */
-  Class getBaseClass() { extend(this, getTypeRef(result)) }
+  Class getBaseClass() {
+    extend(this, getTypeRef(result))
+    or
+    not extend(this, _) and
+    not this instanceof ObjectType and
+    result instanceof ObjectType
+  }
 
   /** Gets an immediate base interface of this type, if any. */
   Interface getABaseInterface() { implement(this, getTypeRef(result)) }