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 92a02ea..a4f425e 100644
--- a/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
+++ b/lib/Dialect/mhlo/transforms/chlo_legalize_to_hlo_patterns.td
@@ -23,10 +23,18 @@ include "mlir-hlo/Dialect/mhlo/IR/chlo_ops.td"
 // Unary op patterns.
 //===----------------------------------------------------------------------===//
 
+def NonComplexElementType : Type<
+  CPred<"!$_self.cast<ShapedType>().getElementType().isa<ComplexType>()">,
+  "Non complex element type">;
+
 // Expand acos to MHLO dialect as follows:
 //   acos(x) = 2 * atan2(sqrt(1 - x^2), (1 + x))  if x != -1
 //           = pi                                 if x == -1
-def : Pat<(HLOClient_AcosOp $input),
+//
+// TODO(hinsu): Support operands with complex element types separately using
+// the following formula.
+//   acos(x) = -(i * log(x + i * sqrt((1 + x) * (1 - x))))
+def : Pat<(HLOClient_AcosOp NonComplexElementType:$input),
   (HLO_SelectOp
     (HLO_CompareOp
       $input,
@@ -68,7 +76,9 @@ def : Pat<(HLOClient_ConjOp $v),
 // Express `sinh` as
 //   sinh(x) = (e^x - e^-x) / 2                     if |x| < 1
 //           = e^(x + log(1/2)) - e^(-x + log(1/2)) otherwise.
-def : Pat<(HLOClient_SinhOp $input),
+// TODO(hinsu): Support operands with complex element types by always using the
+// second formula. The compare op below is not legal for complex numbers.
+def : Pat<(HLOClient_SinhOp NonComplexElementType:$input),
   (HLO_SelectOp
     (HLO_CompareOp
       (HLO_AbsOp $input),