diff --git a/mlir/include/mlir/IR/OpBase.td b/mlir/include/mlir/IR/OpBase.td
--- a/mlir/include/mlir/IR/OpBase.td
+++ b/mlir/include/mlir/IR/OpBase.td
@@ -1503,6 +1503,10 @@
 
   // The list of methods defined by this interface.
   list<InterfaceMethod> methods = [];
+
+  // An optional code block containing extra declarations to place in the
+  // interface declaration.
+  code extraClassDeclaration = "";
 }
 
 // Whether to declare the op interface methods in the op's header. This class
diff --git a/mlir/include/mlir/TableGen/OpInterfaces.h b/mlir/include/mlir/TableGen/OpInterfaces.h
--- a/mlir/include/mlir/TableGen/OpInterfaces.h
+++ b/mlir/include/mlir/TableGen/OpInterfaces.h
@@ -86,6 +86,9 @@
   // Return the description of this method if it has one.
   llvm::Optional<StringRef> getDescription() const;
 
+  // Return the interfaces extra class declaration code.
+  llvm::Optional<StringRef> getExtraClassDeclaration() const;
+
   // Return the verify method body if it has one.
   llvm::Optional<StringRef> getVerify() const;
 
diff --git a/mlir/lib/TableGen/OpInterfaces.cpp b/mlir/lib/TableGen/OpInterfaces.cpp
--- a/mlir/lib/TableGen/OpInterfaces.cpp
+++ b/mlir/lib/TableGen/OpInterfaces.cpp
@@ -86,6 +86,12 @@
   return value.empty() ? llvm::Optional<StringRef>() : value;
 }
 
+// Return the interfaces extra class declaration code.
+llvm::Optional<StringRef> OpInterface::getExtraClassDeclaration() const {
+  auto value = def->getValueAsString("extraClassDeclaration");
+  return value.empty() ? llvm::Optional<StringRef>() : value;
+}
+
 // Return the body for this method if it has one.
 llvm::Optional<StringRef> OpInterface::getVerify() const {
   auto value = def->getValueAsString("verify");
diff --git a/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp b/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
--- a/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
@@ -205,6 +205,11 @@
     emitMethodNameAndArgs(method, os, /*addOperationArg=*/false);
     os << ";\n";
   }
+
+  // Emit any extra declarations.
+  if (Optional<StringRef> extraDecls = interface.getExtraClassDeclaration())
+    os << *extraDecls << "\n";
+
   os << "};\n";
 }