2 files changed, 24 insertions, 1 deletions
diff --git a/tensorflow/cc/framework/gradient_checker.cc b/tensorflow/cc/framework/gradient_checker.cc
index a1eb0d9d08..e9f9c59e3a 100644
--- a/tensorflow/cc/framework/gradient_checker.cc
+++ b/tensorflow/cc/framework/gradient_checker.cc
@@ -351,7 +351,14 @@ Status ComputeGradientErrorInternal(const Scope& scope, const OutputList& xs,
     auto jac_n = jacobian_ns[i].matrix<JAC_T>();
     for (int r = 0; r < jacobian_ts[i].dim_size(0); ++r) {
       for (int c = 0; c < jacobian_ts[i].dim_size(1); ++c) {
-        *max_error = std::max(*max_error, std::fabs(jac_t(r, c) - jac_n(r, c)));
+        auto cur_error = std::fabs(jac_t(r, c) - jac_n(r, c));
+        // Treat any NaN as max_error and immediately return.
+        // (Note that std::max may ignore NaN arguments.)
+        if (std::isnan(cur_error)) {
+          *max_error = cur_error;
+          return Status::OK();
+        }
+        *max_error = std::max(*max_error, cur_error);
       }
     }
   }
diff --git a/tensorflow/cc/framework/gradient_checker_test.cc b/tensorflow/cc/framework/gradient_checker_test.cc
index d4f0a7f5ab..8dd762c282 100644
--- a/tensorflow/cc/framework/gradient_checker_test.cc
+++ b/tensorflow/cc/framework/gradient_checker_test.cc
@@ -28,12 +28,14 @@ namespace {
 
 using ops::Complex;
 using ops::Const;
+using ops::Div;
 using ops::MatMul;
 using ops::Placeholder;
 using ops::Real;
 using ops::Split;
 using ops::Square;
 using ops::Stack;
+using ops::Sub;
 using ops::Unstack;
 
 TEST(GradientCheckerTest, BasicFloat) {
@@ -104,6 +106,20 @@ TEST(GradientCheckerTest, Complex64ToFloat) {
   EXPECT_LT(max_error, 1e-4);
 }
 
+// When calculating gradients that are undefined, test we get NaN
+// as the computed error rather than 0.
+TEST(GradientCheckerTest, BasicNan) {
+  Scope scope = Scope::NewRootScope();
+  TensorShape shape({2, 4, 3});
+  auto x = Placeholder(scope, DT_FLOAT, Placeholder::Shape(shape));
+  // y = x/(x-x) should always return NaN
+  auto y = Div(scope, x, Sub(scope, x, x));
+  float max_error;
+  TF_ASSERT_OK((ComputeGradientError<float, float, float>(
+      scope, {x}, {shape}, {y}, {shape}, &max_error)));
+  EXPECT_TRUE(std::isnan(max_error));
+}
+
 TEST(GradientCheckerTest, MatMulGrad) {
   Scope scope = Scope::NewRootScope();