diff --git a/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td b/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
index fb4bf3a..a48abb6 100644
--- a/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
+++ b/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
@@ -24,16 +24,17 @@ include "mlir-hlo/Dialect/mhlo/IR/chlo_ops.td"
 //===----------------------------------------------------------------------===//
 
 // Expand acos to MHLO dialect as follows:
-//   acos(x) = 2 * atan(sqrt(1 - x^2) / (1 + x))  if x != -1
+//   acos(x) = 2 * atan2(sqrt(1 - x^2), (1 + x))  if x != -1
 //           = pi                                 if x == -1
 def : Pat<(HLOClient_AcosOp $input),
   (HLO_SelectOp
-    (HLO_CompareOp $input,
-      (HLO_ConstantLike<"0"> $input),
+    (HLO_CompareOp
+      $input,
+      (HLO_ConstantLike<"-1"> $input),
       HLO_COMPARISON_DIRECTION_NE
     ),
     (HLO_MulOp
-      (HLO_ConstantLike<"2.0f"> $input),
+      (HLO_ConstantLike<"2"> $input),
       (HLO_Atan2Op
         (HLO_SqrtOp
           (HLO_SubOp
@@ -47,7 +48,8 @@ def : Pat<(HLOClient_AcosOp $input),
         )
       )
     ),
-    (HLO_ConstantLike<"M_PI"> $input))>;
+    (HLO_ConstantLike<"M_PI"> $input)
+  )>;
 
 // Express `atan` as
 //   atan(x) = atan2(x, 1)