diff --git a/tensorflow/cc/framework/gradients.cc b/tensorflow/cc/framework/gradients.cc
index 82469261e5b..ac5b945c947 100644
--- a/tensorflow/cc/framework/gradients.cc
+++ b/tensorflow/cc/framework/gradients.cc
@@ -175,8 +175,14 @@ Status SymbolicGradientBuilder::Initialize() {
         "Must specify a gradient input for each output.");
   }
   std::vector<bool> reachable_nodes = GetReachableNodes();
-  // TODO(theflofly) Check that inputs_ are reachable from
-  // outputs_ using reachable_nodes
+  for (const Output& input : inputs_) {
+    if (!reachable_nodes[input.node()->id()]) {
+      return errors::InvalidArgument(
+        "Cannot compute the partial derivative for node '",
+        input.node()->name(),
+        "' as it's unreachable from the output node(s).");
+    }
+  }
   grad_outputs_->clear();
   grad_outputs_->resize(inputs_.size());
   // Populate `output_nodes_` from node ids in `outputs_`.
diff --git a/tensorflow/cc/framework/gradients_test.cc b/tensorflow/cc/framework/gradients_test.cc
index 032ab936235..f2814683dc9 100644
--- a/tensorflow/cc/framework/gradients_test.cc
+++ b/tensorflow/cc/framework/gradients_test.cc
@@ -48,9 +48,9 @@ class GradientsTest : public ::testing::Test {
   Scope scope_test_;
 };
 
-// EX.
+// Example:
 //      ^             ^
-//    dy|           dx|        // MatMul Gradient Graph
+//    dy|           dx|        (MatMul Gradient Graph)
 //      |             |
 //   MatMul_1      MatMul_2
 //   ^   ^          ^    ^
@@ -61,7 +61,7 @@ class GradientsTest : public ::testing::Test {
 //   |     Const_3       |
 //   |                   |
 //   |        ^          |
-//   |       z|          |     // MatMul Forward Graph
+//   |       z|          |     (MatMul Forward Graph)
 //   |        |          |
 //   |      MatMul_0     |
 //   |     /        \    |
@@ -373,24 +373,22 @@ TEST_F(GradientsTest, UnreachableEdgeGradOneOutput) {
   auto y_const = Const(scope_test_, {{1.0}, {2.0}, {3.0}});
   auto y_assign = Assign(scope_test_, y, y_const);
 
-  auto m1 = MatMul(scope_test_, x, y);
+  auto m = MatMul(scope_test_, x, y);
 
   auto z = Variable(scope_test_, {1, 3}, DT_DOUBLE);
   auto z_const = Const(scope_test_, {{9.0, 10.0, 11.0}});
   auto z_assign = Assign(scope_test_, z, z_const);
 
-  auto m2 = MatMul(scope_test_, y, z);
-
-  auto dm1 = Const(scope_test_, {{0.5}, {0.5}});
+  auto diff_m = Const(scope_test_, {{0.5}, {0.5}});
 
   std::vector<Output> grad_outputs;
   TF_ASSERT_OK(
-      AddSymbolicGradients(scope_test_, {m1}, {y}, {dm1}, &grad_outputs));
+      AddSymbolicGradients(scope_test_, {m}, {y}, {diff_m}, &grad_outputs));
 
   std::vector<Tensor> outputs;
   test::GetTensors(scope_test_, {x_assign, y_assign, z_assign},
                    {grad_outputs[0]}, &outputs);
-  // dz/dy = xT * dm1
+  // dz/dy = xT * diff_m
   test::ExpectTensorNear<double>(
       outputs[0], test::AsTensor<double>({2.5, 3.5, 4.5}, {3, 1}), 1e-5);
 }
@@ -424,13 +422,36 @@ TEST_F(GradientsTest, UnreachableEdgeGradTwoOutputs) {
   test::GetTensors(scope_test_, {x_assign, y_assign, z_assign},
                    {grad_outputs[0]}, &outputs);
 
-  // the gradients from m1 and m2 will be summed to compute the gradient
-  // w.r.t y
+  // The gradients from m1 and m2 will be summed to compute the gradient
+  // w.r.t y:
   // dz/dy = xT * dm1 + dm2 * zT
   test::ExpectTensorNear<double>(
       outputs[0], test::AsTensor<double>({17.5, 24.7, 26.8}, {3, 1}), 1e-5);
 }
 
+TEST_F(GradientsTest, UnreachableInput) {
+  auto x = Const(scope_test_, {{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}});
+  auto y = Const(scope_test_, {{1.0}, {2.0}, {3.0}});
+  auto z = Const(scope_test_.WithOpName("z"), {{9.0, 10.0, 11.0}});
+
+  auto m1 = MatMul(scope_test_, x, y);
+  auto m2 = MatMul(scope_test_, y, z);
+  auto dm1 = Const(scope_test_, {{0.5}, {0.5}});
+  
+  // From m1, z is unreachable, so an error status should be returned.
+  //   m2  m1
+  //   |   |
+  //   *   *
+  //  / \ / \
+  // z   y   x
+  std::vector<Output> grad_outputs;
+  Status status = AddSymbolicGradients(scope_test_, {m1}, {z}, {dm1},
+      &grad_outputs);
+  EXPECT_EQ(status.code(), error::INVALID_ARGUMENT);
+  EXPECT_EQ(status.error_message(), "Cannot compute the partial derivative"
+      " for node 'z' as it's unreachable from the output node(s).");
+}
+
 // StopGradientSingleOutputMultiEdgeTest tests combinations of valid and
 // 'NoGradient' (induced by StopGradient op) returned along multiple edges from
 // a single nodes output.