diff --git a/lib/Dialect/mhlo/transforms/legalize_trigonometric_to_approximation.cc b/lib/Dialect/mhlo/transforms/legalize_trigonometric_to_approximation.cc
index 180bf9d..24058e0 100644
--- a/lib/Dialect/mhlo/transforms/legalize_trigonometric_to_approximation.cc
+++ b/lib/Dialect/mhlo/transforms/legalize_trigonometric_to_approximation.cc
@@ -137,6 +137,8 @@ class ApproximateTanhLowering
         loc, CmpFPredicate::ULT, input,
         rewriter.create<ConstantOp>(
             loc, rewriter.getF32FloatAttr(-7.90531110763549805f)));
+    Value input_is_nan =
+        rewriter.create<CmpFOp>(loc, CmpFPredicate::UNE, input, input);
     approx = rewriter.create<SelectOp>(
         loc, too_large_input,
         rewriter.create<ConstantOp>(loc, rewriter.getF32FloatAttr(1.0)),
@@ -145,6 +147,7 @@ class ApproximateTanhLowering
         loc, too_small_input,
         rewriter.create<ConstantOp>(loc, rewriter.getF32FloatAttr(-1.0)),
         approx);
+    approx = rewriter.create<SelectOp>(loc, input_is_nan, input, approx);
 
     return approx;
   }
diff --git a/tests/legalize-trigonometric-to-approximation.mlir b/tests/legalize-trigonometric-to-approximation.mlir
index 9b77d14..e19c4f0 100644
--- a/tests/legalize-trigonometric-to-approximation.mlir
+++ b/tests/legalize-trigonometric-to-approximation.mlir
@@ -54,9 +54,11 @@ func @tanh_f32(%arg0 : f32) -> f32 {
   // CHECK-DAG: %[[TMP23:.*]] = select %[[TMP22]], %[[ARG]], %[[TMP20]] : f32
   // CHECK-DAG: %[[TMP24:.*]] = cmpf ugt, %[[ARG]], %[[C11]] : f32
   // CHECK-DAG: %[[TMP25:.*]] = cmpf ult, %[[ARG]], %[[C12]] : f32
+  // CHECK-DAG: %[[IS_NAN:.*]] = cmpf une, %[[ARG]], %[[ARG]] : f32
   // CHECK-DAG: %[[TMP26:.*]] = select %[[TMP24]], %[[C13]], %[[TMP23]] : f32
   // CHECK-DAG: %[[TMP27:.*]] = select %[[TMP25]], %[[C14]], %[[TMP26]] : f32
-  // CHECK: return %[[TMP27]] : f32
+  // CHECK-DAG: %[[RESULT:.*]] = select %[[IS_NAN]], %[[ARG]], %[[TMP27]] : f32
+  // CHECK: return %[[RESULT]] : f32
   %res = math.tanh %arg0 : f32
   return %res : f32
 }