diff --git a/mlir/lib/Dialect/StandardOps/Ops.cpp b/mlir/lib/Dialect/StandardOps/Ops.cpp
--- a/mlir/lib/Dialect/StandardOps/Ops.cpp
+++ b/mlir/lib/Dialect/StandardOps/Ops.cpp
@@ -1591,6 +1591,13 @@
   auto cast = dyn_cast_or_null<IndexCastOp>(getOperand().getDefiningOp());
   if (cast && cast.getOperand().getType() == getType())
     return cast.getOperand();
+
+  // Fold IndexCast(constant) -> constant
+  // A little hack because we go through int.  Otherwise, the size
+  // of the constant might need to change.
+  if (auto value = cstOperands[0].dyn_cast_or_null<IntegerAttr>())
+    return IntegerAttr::get(getType(), value.getInt());
+
   return {};
 }
 
diff --git a/mlir/test/Transforms/canonicalize.mlir b/mlir/test/Transforms/canonicalize.mlir
--- a/mlir/test/Transforms/canonicalize.mlir
+++ b/mlir/test/Transforms/canonicalize.mlir
@@ -887,3 +887,15 @@
   // CHECK: return %[[ARG_0]] : i16
   return %12 : i16
 }
+
+// CHECK-LABEL: func @index_cast_fold
+func @index_cast_fold() -> (i16, index) {
+  %c4 = constant 4 : index
+  %1 = index_cast %c4 : index to i16
+  %c4_i16 = constant 4 : i16
+  %2 = index_cast %c4_i16 : i16 to index
+  // CHECK: %[[C4_I16:.*]] = constant 4 : i16
+  // CHECK: %[[C4:.*]] = constant 4 : index
+  // CHECK: return %[[C4_I16]], %[[C4]] : i16, index
+  return %1, %2 : i16, index
+}