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
@@ -2938,6 +2938,9 @@
   // The underlying C++ value type
   let returnType = dialect.cppNamespace # "::" # cppClassName;
 
+  // Make it possible to use such attributes as parameters for other attributes.
+  string cppType = dialect.cppNamespace # "::" # cppClassName;
+
   // The call expression to convert from the storage type to the return
   // type. For example, an enum can be stored as an int but returned as an
   // enum class.
diff --git a/mlir/test/lib/Dialect/Test/TestAttrDefs.td b/mlir/test/lib/Dialect/Test/TestAttrDefs.td
--- a/mlir/test/lib/Dialect/Test/TestAttrDefs.td
+++ b/mlir/test/lib/Dialect/Test/TestAttrDefs.td
@@ -43,6 +43,14 @@
       >: $arrayOfInts
   );
 }
+def CompoundAttrNested : Test_Attr<"CompoundAttrNested"> {
+  let mnemonic = "cmpnd_nested";
+  let parameters = (
+    ins
+    CompoundAttrA : $nested
+  );
+  let assemblyFormat = "`<` `nested` `=` $nested `>`";
+}
 
 // An attribute testing AttributeSelfTypeParameter.
 def AttrWithSelfTypeParam : Test_Attr<"AttrWithSelfTypeParam"> {
diff --git a/mlir/test/lib/Dialect/Test/TestOps.td b/mlir/test/lib/Dialect/Test/TestOps.td
--- a/mlir/test/lib/Dialect/Test/TestOps.td
+++ b/mlir/test/lib/Dialect/Test/TestOps.td
@@ -1902,6 +1902,11 @@
   let assemblyFormat = "$compound attr-dict-with-keyword";
 }
 
+def FormatNestedAttr : TEST_Op<"format_nested_attr"> {
+  let arguments = (ins CompoundAttrNested:$nested);
+  let assemblyFormat = "$nested attr-dict-with-keyword";
+}
+
 //===----------------------------------------------------------------------===//
 // Custom Directives
 
diff --git a/mlir/test/mlir-tblgen/op-format.mlir b/mlir/test/mlir-tblgen/op-format.mlir
--- a/mlir/test/mlir-tblgen/op-format.mlir
+++ b/mlir/test/mlir-tblgen/op-format.mlir
@@ -259,6 +259,14 @@
 // CHECK: test.format_compound_attr #test.cmpnd_a<1, !test.smpla, [5, 6]>
 test.format_compound_attr #test.cmpnd_a<1, !test.smpla, [5, 6]>
 
+// CHECK:  module attributes {test.nested = #test.cmpnd_nested<nested = #test.cmpnd_a<1, !test.smpla, [5, 6]>>} {
+module attributes {test.nested = #test.cmpnd_nested<nested = #test.cmpnd_a<1, !test.smpla, [5, 6]>>} {
+}
+
+// CHECK: test.format_nested_attr #test.cmpnd_nested<nested = #test.cmpnd_a<1, !test.smpla, [5, 6]>>
+test.format_nested_attr #test.cmpnd_nested<nested = #test.cmpnd_a<1, !test.smpla, [5, 6]>>
+
+
 //===----------------------------------------------------------------------===//
 // Format custom directives
 //===----------------------------------------------------------------------===//