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
@@ -967,6 +967,24 @@
   let baseAttr = attr;
 }
 
+// Decorates an optional attribute to have an (unvalidated) default value
+// return by ODS generated accessors if not present.
+class DefaultValuedOptionalAttr<Attr attr, string val> :
+    Attr<attr.predicate, attr.summary> {
+  // Construct this attribute with the input attribute and change only
+  // the default value.
+  // Note: this has to be kept up to date with Attr above.
+  let storageType = attr.storageType;
+  let returnType = attr.returnType;
+  let convertFromStorage = attr.convertFromStorage;
+  let constBuilderCall = attr.constBuilderCall;
+  let defaultValue = val;
+  let valueType = attr.valueType;
+  let isOptional = 1;
+
+  let baseAttr = attr;
+}
+
 // Decorates an attribute as optional. The return type of the generated
 // attribute accessor method will be Optional<>.
 class OptionalAttr<Attr attr> : Attr<attr.predicate, attr.summary> {
diff --git a/mlir/test/mlir-tblgen/op-attribute.td b/mlir/test/mlir-tblgen/op-attribute.td
--- a/mlir/test/mlir-tblgen/op-attribute.td
+++ b/mlir/test/mlir-tblgen/op-attribute.td
@@ -158,7 +158,7 @@
 def AgetOp : Op<Test2_Dialect, "a_get_op", []> {
   let arguments = (ins
       SomeAttr:$aAttr,
-      DefaultValuedAttr<SomeAttr, "4.2">:$bAttr,
+      DefaultValuedOptionalAttr<SomeAttr, "4.2">:$bAttr,
       OptionalAttr<SomeAttr>:$cAttr
   );
 }
@@ -255,7 +255,7 @@
 // DEF-NEXT:     odsState.addAttribute(getCAttrAttrName(odsState.name), cAttr);
 
 // DEF:      void AgetOp::build(
-// DEF:        some-return-type aAttr, some-return-type bAttr, /*optional*/some-attr-kind cAttr
+// DEF:        some-return-type aAttr, /*optional*/some-return-type bAttr, /*optional*/some-attr-kind cAttr
 // DEF:        odsState.addAttribute(getAAttrAttrName(odsState.name), some-const-builder-call(odsBuilder, aAttr));
 
 // DEF:      void AgetOp::build(