diff --git a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
--- a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
+++ b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
@@ -713,10 +713,10 @@
   let verifier = [{ return ::verify(*this); }];
 }
 
-def Shape_AssumingOp : Shape_Op<"assuming",
-                           [SingleBlockImplicitTerminator<"AssumingYieldOp">,
-                            DeclareOpInterfaceMethods<RegionBranchOpInterface>,
-                            RecursiveSideEffects]> {
+def Shape_AssumingOp : Shape_Op<"assuming", [
+    SingleBlockImplicitTerminator<"AssumingYieldOp">,
+    DeclareOpInterfaceMethods<RegionBranchOpInterface>,
+    RecursiveSideEffects]> {
   let summary = "Execute the region";
   let description = [{
     Executes the region assuming all witnesses are true.
@@ -742,6 +742,11 @@
     static void inlineRegionIntoParent(AssumingOp &op, PatternRewriter &rewriter);
   }];
 
+  let builders = [
+    OpBuilder<(ins "Value":$witness,
+        CArg<"function_ref<SmallVector<Value, 2>(OpBuilder &, Location)>">)>
+  ];
+
   let hasCanonicalizer = 1;
 }
 
@@ -757,7 +762,9 @@
 
   let arguments = (ins Variadic<AnyType>:$operands);
 
-  let builders = [OpBuilder<(ins), [{ /* nothing to do */ }]>];
+  let builders = [
+    OpBuilder<(ins), [{ /* nothing to do */ }]>,
+  ];
 
   let assemblyFormat = "attr-dict ($operands^ `:` type($operands))?";
 }
diff --git a/mlir/lib/Dialect/Shape/IR/Shape.cpp b/mlir/lib/Dialect/Shape/IR/Shape.cpp
--- a/mlir/lib/Dialect/Shape/IR/Shape.cpp
+++ b/mlir/lib/Dialect/Shape/IR/Shape.cpp
@@ -311,6 +311,27 @@
   rewriter.mergeBlocks(blockAfterAssuming, blockBeforeAssuming);
 }
 
+void AssumingOp::build(
+    OpBuilder &builder, OperationState &result, Value witness,
+    function_ref<SmallVector<Value, 2>(OpBuilder &, Location)> bodyBuilder) {
+
+  result.addOperands(witness);
+  Region *bodyRegion = result.addRegion();
+  bodyRegion->push_back(new Block);
+  Block &bodyBlock = bodyRegion->front();
+
+  // Build body.
+  OpBuilder::InsertionGuard guard(builder);
+  builder.setInsertionPointToStart(&bodyBlock);
+  SmallVector<Value, 2> yieldValues = bodyBuilder(builder, result.location);
+  builder.create<AssumingYieldOp>(result.location, yieldValues);
+
+  SmallVector<Type, 2> assumingTypes;
+  for (Value v : yieldValues)
+    assumingTypes.push_back(v.getType());
+  result.addTypes(assumingTypes);
+}
+
 //===----------------------------------------------------------------------===//
 // AssumingAllOp
 //===----------------------------------------------------------------------===//