diff --git a/mlir/lib/Conversion/ShapeToStandard/ShapeToStandard.cpp b/mlir/lib/Conversion/ShapeToStandard/ShapeToStandard.cpp
--- a/mlir/lib/Conversion/ShapeToStandard/ShapeToStandard.cpp
+++ b/mlir/lib/Conversion/ShapeToStandard/ShapeToStandard.cpp
@@ -91,6 +91,19 @@
   }
 };
 
+class ConstSizeOpConverter : public OpConversionPattern<shape::ConstSizeOp> {
+public:
+  using OpConversionPattern<shape::ConstSizeOp>::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(shape::ConstSizeOp op, ArrayRef<Value> operands,
+                  ConversionPatternRewriter &rewriter) const override {
+    rewriter.replaceOpWithNewOp<ConstantIndexOp>(op.getOperation(),
+                                                 op.value().getSExtValue());
+    return success();
+  }
+};
+
 /// Type conversions.
 class ShapeTypeConverter : public TypeConverter {
 public:
@@ -111,9 +124,7 @@
 /// Conversion pass.
 class ConvertShapeToStandardPass
     : public ConvertShapeToStandardBase<ConvertShapeToStandardPass> {
-
   void runOnOperation() override {
-
     // Setup type conversion.
     MLIRContext &ctx = getContext();
     ShapeTypeConverter typeConverter(&ctx);
@@ -146,6 +157,7 @@
   patterns.insert<
       BinaryOpConversion<AddOp, AddIOp>,
       BinaryOpConversion<MulOp, MulIOp>,
+      ConstSizeOpConverter,
       FromExtentTensorOpConversion,
       IndexToSizeOpConversion,
       SizeToIndexOpConversion,
diff --git a/mlir/test/Conversion/ShapeToStandard/shape-to-standard.mlir b/mlir/test/Conversion/ShapeToStandard/shape-to-standard.mlir
--- a/mlir/test/Conversion/ShapeToStandard/shape-to-standard.mlir
+++ b/mlir/test/Conversion/ShapeToStandard/shape-to-standard.mlir
@@ -75,3 +75,14 @@
   // CHECK-NEXT: muli %[[LHS]], %[[RHS]] : index
   return
 }
+
+// -----
+
+// Convert `const_size` to `constant` op.
+// CHECK-LABEL: @size_const
+func @size_const() -> !shape.size {
+  %c1 = shape.const_size 1
+  return %c1 : !shape.size
+}
+// CHECK: %[[C1:.*]] = constant 1 : index
+// CHECK: return %[[C1]] : index