Index: mlir/include/mlir/IR/Attributes.h
===================================================================
--- mlir/include/mlir/IR/Attributes.h
+++ mlir/include/mlir/IR/Attributes.h
@@ -266,7 +266,8 @@
 };
 template <typename T>
 struct DenseMapInfo<
-    T, std::enable_if_t<std::is_base_of<mlir::Attribute, T>::value>>
+    T, std::enable_if_t<std::is_base_of<mlir::Attribute, T>::value &&
+                        !mlir::detail::IsInterface<T>::value>>
     : public DenseMapInfo<mlir::Attribute> {
   static T getEmptyKey() {
     const void *pointer = llvm::DenseMapInfo<const void *>::getEmptyKey();
Index: mlir/include/mlir/IR/OpDefinition.h
===================================================================
--- mlir/include/mlir/IR/OpDefinition.h
+++ mlir/include/mlir/IR/OpDefinition.h
@@ -1963,8 +1963,9 @@
 namespace llvm {
 
 template <typename T>
-struct DenseMapInfo<
-    T, std::enable_if_t<std::is_base_of<mlir::OpState, T>::value>> {
+struct DenseMapInfo<T,
+                    std::enable_if_t<std::is_base_of<mlir::OpState, T>::value &&
+                                     !mlir::detail::IsInterface<T>::value>> {
   static inline T getEmptyKey() {
     auto *pointer = llvm::DenseMapInfo<void *>::getEmptyKey();
     return T::getFromOpaquePointer(pointer);
Index: mlir/include/mlir/IR/Types.h
===================================================================
--- mlir/include/mlir/IR/Types.h
+++ mlir/include/mlir/IR/Types.h
@@ -282,7 +282,8 @@
   static bool isEqual(mlir::Type LHS, mlir::Type RHS) { return LHS == RHS; }
 };
 template <typename T>
-struct DenseMapInfo<T, std::enable_if_t<std::is_base_of<mlir::Type, T>::value>>
+struct DenseMapInfo<T, std::enable_if_t<std::is_base_of<mlir::Type, T>::value &&
+                                        !mlir::detail::IsInterface<T>::value>>
     : public DenseMapInfo<mlir::Type> {
   static T getEmptyKey() {
     const void *pointer = llvm::DenseMapInfo<const void *>::getEmptyKey();
Index: mlir/include/mlir/Support/InterfaceSupport.h
===================================================================
--- mlir/include/mlir/Support/InterfaceSupport.h
+++ mlir/include/mlir/Support/InterfaceSupport.h
@@ -78,6 +78,7 @@
       Interface<ConcreteType, ValueT, Traits, BaseType, BaseTrait>;
   template <typename T, typename U>
   using ExternalModel = typename Traits::template ExternalModel<T, U>;
+  using ValueType = ValueT;
 
   /// This is a special trait that registers a given interface with an object.
   template <typename ConcreteT>
@@ -104,6 +105,9 @@
     assert((!t || impl) && "expected value to provide interface instance");
   }
 
+  /// Constructor for DenseMapInfo's empty key and tombstone key.
+  Interface(ValueT t, std::nullptr_t) : BaseType(t), impl(nullptr) {}
+
   /// Support 'classof' by checking if the given object defines the concrete
   /// interface.
   static bool classof(ValueT t) { return ConcreteType::getInterfaceFor(t); }
@@ -264,7 +268,37 @@
   SmallVector<std::pair<TypeID, void *>> interfaces;
 };
 
+template <typename ConcreteType, typename ValueT, typename Traits,
+          typename BaseType,
+          template <typename, template <typename> class> class BaseTrait>
+void isInterfaceImpl(
+    Interface<ConcreteType, ValueT, Traits, BaseType, BaseTrait> &);
+
+template <class T>
+using is_interface_t = decltype(isInterfaceImpl(std::declval<T&>()));
+
+template <class T>
+using IsInterface = llvm::is_detected<is_interface_t, T>;
+
 } // namespace detail
 } // namespace mlir
 
+template <class T>
+struct llvm::DenseMapInfo<
+    T, std::enable_if_t<mlir::detail::IsInterface<T>::value>> {
+  using ValueTypeInfo = llvm::DenseMapInfo<typename T::ValueType>;
+
+  static T getEmptyKey() { return T(ValueTypeInfo::getEmptyKey(), nullptr); }
+
+  static T getTombstoneKey() {
+    return T(ValueTypeInfo::getTombstoneKey(), nullptr);
+  }
+
+  static unsigned getHashValue(T val) {
+    return ValueTypeInfo::getHashValue(val);
+  }
+
+  static bool isEqual(T lhs, T rhs) { return ValueTypeInfo::isEqual(lhs, rhs); }
+};
+
 #endif
Index: mlir/unittests/IR/CMakeLists.txt
===================================================================
--- mlir/unittests/IR/CMakeLists.txt
+++ mlir/unittests/IR/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_mlir_unittest(MLIRIRTests
   AttributeTest.cpp
   DialectTest.cpp
+  InterfaceTest.cpp
   InterfaceAttachmentTest.cpp
   OperationSupportTest.cpp
   PatternMatchTest.cpp
Index: mlir/unittests/IR/InterfaceTest.cpp
===================================================================
--- mlir/unittests/IR/InterfaceTest.cpp
+++ mlir/unittests/IR/InterfaceTest.cpp
@@ -1,3 +1,45 @@
+//===- InterfaceTest.cpp - Test interfaces --------------------------------===//
 //
-// Created by Markus Böck on 02/07/2022.
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
+//===----------------------------------------------------------------------===//
+
+#include "mlir/IR/BuiltinAttributes.h"
+#include "mlir/IR/BuiltinDialect.h"
+#include "mlir/IR/BuiltinOps.h"
+#include "mlir/IR/BuiltinTypes.h"
+#include "gtest/gtest.h"
+
+#include "../../test/lib/Dialect/Test/TestAttributes.h"
+#include "../../test/lib/Dialect/Test/TestDialect.h"
+#include "../../test/lib/Dialect/Test/TestTypes.h"
+#include "mlir/IR/OwningOpRef.h"
+
+using namespace mlir;
+using namespace test;
+
+TEST(InterfaceTest, DenseMapKey) {
+  DialectRegistry registry;
+  registry.insert<test::TestDialect>();
+
+  MLIRContext context(registry);
+  context.loadDialect<test::TestDialect>();
+
+  OwningOpRef<ModuleOp> module = ModuleOp::create(UnknownLoc::get(&context));
+  OpBuilder builder(module->getBody(), module->getBody()->begin());
+  auto op1 = builder.create<test::SideEffectOp>(builder.getUnknownLoc(),
+                                                builder.getI32Type());
+  auto op2 = builder.create<test::SideEffectOp>(builder.getUnknownLoc(),
+                                                builder.getI32Type());
+  auto op3 = builder.create<test::SideEffectOp>(builder.getUnknownLoc(),
+                                                builder.getI32Type());
+  DenseSet<MemoryEffectOpInterface> set;
+  set.insert(op1);
+  set.insert(op2);
+  set.erase(op1);
+  EXPECT_FALSE(set.contains(op1));
+  EXPECT_TRUE(set.contains(op2));
+  EXPECT_FALSE(set.contains(op3));
+}