diff --git a/reverb/cc/trajectory_writer.cc b/reverb/cc/trajectory_writer.cc
index b5645ad..afc2478 100644
--- a/reverb/cc/trajectory_writer.cc
+++ b/reverb/cc/trajectory_writer.cc
@@ -14,6 +14,7 @@
 
 #include "reverb/cc/trajectory_writer.h"
 
+#include <cmath>
 #include <limits>
 #include <memory>
 #include <vector>
@@ -430,6 +431,9 @@ absl::Status TrajectoryWriter::CreateItem(
                   [](const TrajectoryColumn& col) { return col.empty(); })) {
     return absl::InvalidArgumentError("trajectory must not be empty.");
   }
+  if (std::isnan(priority)) {
+    return absl::InvalidArgumentError("`priority` must not be nan.");
+  }
 
   {
     absl::MutexLock lock(&mu_);
diff --git a/reverb/cc/trajectory_writer_test.cc b/reverb/cc/trajectory_writer_test.cc
index 498d05c..1541520 100644
--- a/reverb/cc/trajectory_writer_test.cc
+++ b/reverb/cc/trajectory_writer_test.cc
@@ -13,8 +13,10 @@
 // limitations under the License.
 
 #include "reverb/cc/trajectory_writer.h"
+
 #include <grpcpp/support/status.h>
 
+#include <cmath>
 #include <limits>
 #include <memory>
 #include <string>
@@ -1358,6 +1360,24 @@ TEST(TrajectoryWriter, CreateItemValidatesSqueezedColumns) {
                            "exactly one row when squeeze is set but got 2."));
 }
 
+TEST(TrajectoryWriter, CreateItemValidatesPriorityIsNotNan) {
+  AsyncInterface success_stream;
+  auto stub = std::make_shared<MockReverbServiceAsyncStub>();
+  EXPECT_CALL(*stub, async()).WillRepeatedly(Return(&success_stream));
+
+  TrajectoryWriter writer(
+      stub, MakeOptions(/*max_chunk_length=*/1, /*num_keep_alive_refs=*/1));
+
+  StepRef step;
+  REVERB_ASSERT_OK(writer.Append(Step({MakeTensor(kIntSpec)}), &step));
+
+  auto status =
+      writer.CreateItem("table", std::nan("1"), MakeTrajectory({step}));
+  EXPECT_EQ(status.code(), absl::StatusCode::kInvalidArgument);
+  EXPECT_THAT(std::string(status.message()),
+              ::testing::HasSubstr("`priority` must not be nan."));
+}
+
 class TrajectoryWriterSignatureValidationTest : public ::testing::Test {
  protected:
   void SetUp() override {
diff --git a/reverb/cc/writer.cc b/reverb/cc/writer.cc
index b61cfa4..308aacf 100644
--- a/reverb/cc/writer.cc
+++ b/reverb/cc/writer.cc
@@ -15,6 +15,7 @@
 #include "reverb/cc/writer.h"
 
 #include <algorithm>
+#include <cmath>
 #include <iterator>
 #include <memory>
 #include <string>
@@ -169,6 +170,9 @@ absl::Status Writer::CreateItem(const std::string& table, int num_timesteps,
     return absl::InvalidArgumentError(
         "`num_timesteps` must be <= `max_timesteps`");
   }
+  if (std::isnan(priority)) {
+    return absl::InvalidArgumentError("`priority` must not be nan.");
+  }
 
   const internal::DtypesAndShapes* dtypes_and_shapes = nullptr;
   REVERB_RETURN_IF_ERROR(GetFlatSignature(table, &dtypes_and_shapes));
diff --git a/reverb/cc/writer_test.cc b/reverb/cc/writer_test.cc
index 212d616..e6997b4 100644
--- a/reverb/cc/writer_test.cc
+++ b/reverb/cc/writer_test.cc
@@ -15,6 +15,7 @@
 #include "reverb/cc/writer.h"
 
 #include <algorithm>
+#include <cmath>
 #include <memory>
 #include <queue>
 #include <string>
@@ -854,6 +855,25 @@ TEST(WriterTest, WriteTimeStepsInconsistentShapeError) {
                   "dtype float and shape compatible with [5]"));
 }
 
+TEST(WriterTest, WriteNanPriorityError) {
+  std::vector<InsertStreamRequest> requests;
+  auto stub = MakeGoodStub(&requests);
+  Client client(stub);
+  std::unique_ptr<Writer> writer;
+  REVERB_EXPECT_OK(client.NewWriter(2, 6, /*delta_encoded=*/false, &writer));
+
+  REVERB_ASSERT_OK(writer->Append(
+      MakeTimestep(/*num_tensors=*/1, /*shape=*/tensorflow::TensorShape({1}))));
+  REVERB_ASSERT_OK(writer->Append(
+      MakeTimestep(/*num_tensors=*/1, /*shape=*/tensorflow::TensorShape({1}))));
+
+  auto status = writer->CreateItem("dist", 2, std::nan("1"));
+
+  EXPECT_EQ(status.code(), absl::StatusCode::kInvalidArgument);
+  EXPECT_THAT(std::string(status.message()),
+              ::testing::HasSubstr("`priority` must not be nan."));
+}
+
 TEST(WriterTest, WriteTimeStepsInconsistentShapeErrorAgainstBoundedSpec) {
   std::vector<InsertStreamRequest> requests;
   tensorflow::StructuredValue signature = MakeBoundedTensorSpecSignature(