diff --git a/mlir/include/mlir/IR/Dialect.h b/mlir/include/mlir/IR/Dialect.h
index db5ba53ad535..2bb672596212 100644
--- a/mlir/include/mlir/IR/Dialect.h
+++ b/mlir/include/mlir/IR/Dialect.h
@@ -127,11 +127,10 @@ public:
   static bool isValidNamespace(StringRef str);
 
 protected:
-  /// Note: The namePrefix can be empty, but it must not contain '.' characters.
-  /// Note: If the name is non empty, then all operations belonging to this
-  /// dialect will need to start with the namePrefix followed by a '.'.
+  /// Note: The namePrefix must not contain '.' characters.
+  /// Note: All operations belonging to this dialect will need to have names
+  ///       starting with the namePrefix followed by '.'.
   /// Example:
-  ///       - "" for the standard operation set.
   ///       - "tf" for the TensorFlow ops like "tf.add".
   Dialect(StringRef namePrefix, MLIRContext *context);
 
diff --git a/mlir/lib/IR/MLIRContext.cpp b/mlir/lib/IR/MLIRContext.cpp
index aee0ac96917e..9db18f9fd5e2 100644
--- a/mlir/lib/IR/MLIRContext.cpp
+++ b/mlir/lib/IR/MLIRContext.cpp
@@ -704,6 +704,11 @@ void Dialect::registerDialect(MLIRContext *context) {
 
   // Lock access to the context registry.
   llvm::sys::SmartScopedWriter<true> registryLock(impl.contextMutex);
+  assert(llvm::none_of(impl.dialects,
+                       [this](std::unique_ptr<Dialect> &dialect) {
+                         return dialect->getNamespace() == getNamespace();
+                       }) &&
+         "a dialect with the given namespace has already been registered");
   impl.dialects.push_back(std::unique_ptr<Dialect>(this));
 }
 
@@ -737,7 +742,7 @@ std::vector<AbstractOperation *> MLIRContext::getRegisteredOperations() {
 }
 
 void Dialect::addOperation(AbstractOperation opInfo) {
-  assert((namePrefix.empty() || (opInfo.name.split('.').first == namePrefix)) &&
+  assert(opInfo.name.split('.').first == namePrefix &&
          "op name doesn't start with dialect prefix");
   assert(&opInfo.dialect == this && "Dialect object mismatch");
   auto &impl = context->getImpl();
diff --git a/mlir/unittests/IR/DialectTest.cpp b/mlir/unittests/IR/DialectTest.cpp
new file mode 100644
index 000000000000..89b641df15e5
--- /dev/null
+++ b/mlir/unittests/IR/DialectTest.cpp
@@ -0,0 +1,38 @@
+//===- DialectTest.cpp - Dialect unit tests -------------------------------===//
+//
+// Copyright 2019 The MLIR Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// =============================================================================
+
+#include "mlir/IR/Dialect.h"
+#include "gtest/gtest.h"
+
+using namespace mlir;
+using namespace mlir::detail;
+
+namespace {
+struct TestDialect : public Dialect {
+  TestDialect(MLIRContext *context) : Dialect(/*namePrefix=*/"test", context) {}
+};
+
+TEST(DialectDeathTest, MultipleDialectsWithSameNamespace) {
+  MLIRContext context;
+
+  // Registering a dialect with the same namespace twice should result in a
+  // failure.
+  new TestDialect(&context);
+  ASSERT_DEATH(new TestDialect(&context), "");
+}
+
+} // end namespace