diff --git a/tensorflow/core/api_def/base_api/api_def_Cos.pbtxt b/tensorflow/core/api_def/base_api/api_def_Cos.pbtxt
index 19903c53703..383d8681b6e 100644
--- a/tensorflow/core/api_def/base_api/api_def_Cos.pbtxt
+++ b/tensorflow/core/api_def/base_api/api_def_Cos.pbtxt
@@ -4,7 +4,8 @@ op {
   description: << END
   Given an input tensor, this function computes cosine of every
   element in the tensor. Input range is `(-inf, inf)` and
-  output range is `[-1,1]`.
+  output range is `[-1,1]`. If input lies outside the boundary, `nan`
+  is returned.
 
   ```python
   x = tf.constant([-float("inf"), -9, -0.5, 1, 1.2, 200, 10000, float("inf")])
diff --git a/tensorflow/core/api_def/base_api/api_def_Tan.pbtxt b/tensorflow/core/api_def/base_api/api_def_Tan.pbtxt
index 723ad462adb..8a972ba3d86 100644
--- a/tensorflow/core/api_def/base_api/api_def_Tan.pbtxt
+++ b/tensorflow/core/api_def/base_api/api_def_Tan.pbtxt
@@ -4,7 +4,8 @@ op {
   description: << END
   Given an input tensor, this function computes tangent of every
   element in the tensor. Input range is `(-inf, inf)` and
-  output range is `(-inf, inf)`.
+  output range is `(-inf, inf)`. If input lies outside the boundary, `nan`
+  is returned.
 
   ```python
   x = tf.constant([-float("inf"), -9, -0.5, 1, 1.2, 200, 10000, float("inf")])