diff --git a/lib/Filesystem.php b/lib/Filesystem.php
index bc2e01ee..b80aac89 100644
--- a/lib/Filesystem.php
+++ b/lib/Filesystem.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class Filesystem {
   public static function createTemporaryFile(
     string $prefix = '',
diff --git a/lib/Str.php b/lib/Str.php
index cb5775c4..b7567054 100644
--- a/lib/Str.php
+++ b/lib/Str.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class Str {
   public static function explode(
     string $delimiter,
diff --git a/lib/StrBuffer.php b/lib/StrBuffer.php
index a64a1ad3..202faaef 100644
--- a/lib/StrBuffer.php
+++ b/lib/StrBuffer.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 class StrBuffer {
 
   private string $str = '';
diff --git a/lib/utils.php b/lib/utils.php
index f960b08b..e89fa397 100644
--- a/lib/utils.php
+++ b/lib/utils.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Remove the 'HH\' prefix from typehint strings
  * and from strings produced by var_export().
diff --git a/src/BaseCodeBuilder.php b/src/BaseCodeBuilder.php
index f2e4f1aa..8fb37ee4 100644
--- a/src/BaseCodeBuilder.php
+++ b/src/BaseCodeBuilder.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 abstract class BaseCodeBuilder implements ICodeBuilder {
 
   const string DELIMITER = "\t";
diff --git a/src/CodegenClass.php b/src/CodegenClass.php
index 43d7e272..9ef2c7da 100644
--- a/src/CodegenClass.php
+++ b/src/CodegenClass.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a class. Please don't use this class directly; instead use
  * the function codegen_class.  E.g.:
diff --git a/src/CodegenClassBase.php b/src/CodegenClassBase.php
index 55f2e498..a313c1a1 100644
--- a/src/CodegenClassBase.php
+++ b/src/CodegenClassBase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Abstract class to generate code for a class or trait.
  *
diff --git a/src/CodegenConstructor.php b/src/CodegenConstructor.php
index 43476afc..2fb6184a 100644
--- a/src/CodegenConstructor.php
+++ b/src/CodegenConstructor.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a constructor. E.g.
  *
diff --git a/src/CodegenEnum.php b/src/CodegenEnum.php
index b5385e90..aaf8ba0b 100644
--- a/src/CodegenEnum.php
+++ b/src/CodegenEnum.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for an enum. Please don't use this class directly; instead use
  * the function codegen_enum.  E.g.:
diff --git a/src/CodegenFile.php b/src/CodegenFile.php
index 4ba43820..7bb74e54 100644
--- a/src/CodegenFile.php
+++ b/src/CodegenFile.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 enum CodegenFileResult: int {
   NONE = 0;
   UPDATE = 1;
diff --git a/src/CodegenFunction.php b/src/CodegenFunction.php
index 5bbd84d8..2371012b 100644
--- a/src/CodegenFunction.php
+++ b/src/CodegenFunction.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a function. Please don't use this class directly; instead
  * use the function codegen_function.  E.g.:
diff --git a/src/CodegenFunctionBase.php b/src/CodegenFunctionBase.php
index c76477c6..eae43369 100644
--- a/src/CodegenFunctionBase.php
+++ b/src/CodegenFunctionBase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Base class to generate a function or a method.
  */
diff --git a/src/CodegenGeneratedFrom.php b/src/CodegenGeneratedFrom.php
index 722abf6e..d2b89063 100644
--- a/src/CodegenGeneratedFrom.php
+++ b/src/CodegenGeneratedFrom.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Describes how the code was generated in order to write a comment on
  * the generated file.
diff --git a/src/CodegenImplementsInterface.php b/src/CodegenImplementsInterface.php
index f52e37c5..4d9841ac 100644
--- a/src/CodegenImplementsInterface.php
+++ b/src/CodegenImplementsInterface.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Describes an implemented interface, optionally including a comment, like:
  *
diff --git a/src/CodegenInterface.php b/src/CodegenInterface.php
index 3a4f45c2..ca960b5b 100644
--- a/src/CodegenInterface.php
+++ b/src/CodegenInterface.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for an interface. Please don't use this class directly; instead
  * use the function codegen_interface.  E.g.:
diff --git a/src/CodegenMemberVar.php b/src/CodegenMemberVar.php
index 13963251..9ae07e07 100644
--- a/src/CodegenMemberVar.php
+++ b/src/CodegenMemberVar.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a member variable. Please don't use this class directly;
  * instead use the function codegen_member_var.  E.g.:
diff --git a/src/CodegenMethod.php b/src/CodegenMethod.php
index 33fba5b9..88093b75 100644
--- a/src/CodegenMethod.php
+++ b/src/CodegenMethod.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a method. Please don't use this class directly; instead use
  * the function codegen_method.  E.g.:
diff --git a/src/CodegenMethodBase.php b/src/CodegenMethodBase.php
index a583b97a..9872bab4 100644
--- a/src/CodegenMethodBase.php
+++ b/src/CodegenMethodBase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Base class to generate a method or a constructor.
  * See CodegenMethod or CodegenConstructor
diff --git a/src/CodegenShape.php b/src/CodegenShape.php
index b20d0312..760a730c 100644
--- a/src/CodegenShape.php
+++ b/src/CodegenShape.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a shape. Please don't use this class directly; instead use
  * the function codegen_shape.  E.g.:
diff --git a/src/CodegenTrait.php b/src/CodegenTrait.php
index 3ba0aa88..7b882d88 100644
--- a/src/CodegenTrait.php
+++ b/src/CodegenTrait.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a trait. Please don't use this class directly; instead use
  * the function codegen_trait.  E.g.:
diff --git a/src/CodegenType.php b/src/CodegenType.php
index b833a1da..1f548e88 100644
--- a/src/CodegenType.php
+++ b/src/CodegenType.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Generate code for a type or newtype definition. Please don't use this class
  * directly; instead use the functions codegen_type or codegen_newtype. E.g.:
diff --git a/src/CodegenUsesTrait.php b/src/CodegenUsesTrait.php
index 07969c09..6e0f9413 100644
--- a/src/CodegenUsesTrait.php
+++ b/src/CodegenUsesTrait.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Describe an used trait, optionally including a comment, like:
  *
diff --git a/src/CodegenWithVisibility.php b/src/CodegenWithVisibility.php
index 0fbc9d19..ef979749 100644
--- a/src/CodegenWithVisibility.php
+++ b/src/CodegenWithVisibility.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 enum CodegenPHPMethodVisibility : string as string {
   V_PUBLIC = 'public';
   V_PRIVATE = 'private';
diff --git a/src/HackBuilder.php b/src/HackBuilder.php
index 820228c7..13808e1a 100644
--- a/src/HackBuilder.php
+++ b/src/HackBuilder.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Class to facilitate building code. It has methods for some common patterns
  * used to generate code. It also deals with indentation and new lines.
diff --git a/src/HackBuilderKeys.php b/src/HackBuilderKeys.php
index 22e4dd0e..bd56bb49 100644
--- a/src/HackBuilderKeys.php
+++ b/src/HackBuilderKeys.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 enum HackBuilderKeys : int {
   // The key will be used literally, which is useful for example when
   // passing a constant such as MyEnum::Value
diff --git a/src/HackBuilderRenderer.php b/src/HackBuilderRenderer.php
index 6fd032e5..62826822 100644
--- a/src/HackBuilderRenderer.php
+++ b/src/HackBuilderRenderer.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Use this trait along with an implementation of ICodeBuilderRenderer.
  */
diff --git a/src/HackBuilderValues.php b/src/HackBuilderValues.php
index d04d8642..834b64ed 100644
--- a/src/HackBuilderValues.php
+++ b/src/HackBuilderValues.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 enum HackBuilderValues : int {
   // The value will be used literally, which is useful for example when
   // passing a constant such as MyEnum::Value
diff --git a/src/HackCodegenConfig.php b/src/HackCodegenConfig.php
index adede5a2..196b9df2 100644
--- a/src/HackCodegenConfig.php
+++ b/src/HackCodegenConfig.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * This class contains the default configuration for Hack code generation.
  * Please update it to your needs.
diff --git a/src/ICodeBuilder.php b/src/ICodeBuilder.php
index 88b1f37b..b749f3cd 100644
--- a/src/ICodeBuilder.php
+++ b/src/ICodeBuilder.php
@@ -8,5 +8,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 interface ICodeBuilder {
 }
diff --git a/src/ICodeBuilderRenderer.php b/src/ICodeBuilderRenderer.php
index 3bca87f4..3e31cf60 100644
--- a/src/ICodeBuilderRenderer.php
+++ b/src/ICodeBuilderRenderer.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 interface ICodeBuilderRenderer {
   /**
    * Appends the code of this class to the builder
diff --git a/src/ICodegenFormatter.php b/src/ICodegenFormatter.php
index 7872a840..55f164d4 100644
--- a/src/ICodegenFormatter.php
+++ b/src/ICodegenFormatter.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Implement this interface to define a class to format a file after the
  * code is generated.
diff --git a/src/IHackCodegenConfig.php b/src/IHackCodegenConfig.php
index 5c97e28b..132a09c9 100644
--- a/src/IHackCodegenConfig.php
+++ b/src/IHackCodegenConfig.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Implement this interface to define a configuration to generate code.
  * The config will need to be passed to some of the Codegen constructors,
diff --git a/src/PartiallyGeneratedCode.php b/src/PartiallyGeneratedCode.php
index 0923aece..70b94e85 100644
--- a/src/PartiallyGeneratedCode.php
+++ b/src/PartiallyGeneratedCode.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * Manage partially generated code.  The main operation is to merge existing
  * code (that probably has some handwritten code) with generated code.
diff --git a/src/PartiallyGeneratedSignedSource.php b/src/PartiallyGeneratedSignedSource.php
index eb50cf08..1240a4f5 100644
--- a/src/PartiallyGeneratedSignedSource.php
+++ b/src/PartiallyGeneratedSignedSource.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 
 /**
  * Similar to SignedSource, but it uses a different header to indicate that the
diff --git a/src/SignedSource.php b/src/SignedSource.php
index e466e47c..530d1860 100644
--- a/src/SignedSource.php
+++ b/src/SignedSource.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  *  Designate machine-generated code so tools can distinguish it from
  *  human-generated code, and prevent manual edits of machine-generated code by
diff --git a/src/SignedSourceBase.php b/src/SignedSourceBase.php
index d098936a..9f2609b6 100644
--- a/src/SignedSourceBase.php
+++ b/src/SignedSourceBase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 abstract class SignedSourceBase {
 
   const TOKEN   ='<<SignedSource::*O*zOeWoEQle#+L!plEphiEmie@I>>';
diff --git a/test/CodegenBaseTest.php b/test/CodegenBaseTest.php
index ef5e55a7..1fc5695d 100644
--- a/test/CodegenBaseTest.php
+++ b/test/CodegenBaseTest.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 abstract class CodegenBaseTest {
 
   public static function assertTrue(
diff --git a/test/CodegenClassTestCase.codegen b/test/CodegenClassTestCase.codegen
index 43678dda..e3de12db 100644
--- a/test/CodegenClassTestCase.codegen
+++ b/test/CodegenClassTestCase.codegen
@@ -8,6 +8,8 @@ class ClassWithGenerics
   > {
 }
 
+namespace Facebook/HackCodegen;
+
 !@#$%codegentest:testConstructorWrapperFunc
 function TestWrapperFunc(string $text, ?bool $hack): TestWrapperFunc {
   return new TestWrapperFunc($text, $hack);
diff --git a/test/CodegenClassTestCase.php b/test/CodegenClassTestCase.php
index 5e58afc1..f9e4e57d 100644
--- a/test/CodegenClassTestCase.php
+++ b/test/CodegenClassTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenClassTestCase extends CodegenBaseTest {
 
   public function testDocblock() {
diff --git a/test/CodegenEnumTestCase.codegen b/test/CodegenEnumTestCase.codegen
index 376b6c0a..ff8a59fa 100644
--- a/test/CodegenEnumTestCase.codegen
+++ b/test/CodegenEnumTestCase.codegen
@@ -8,6 +8,8 @@ enum Demo : string {
    * This is a different letter
    */
   B = 'b';
+namespace Facebook/HackCodegen;
+
 }
 
 !@#$%codegentest:testDocblock
diff --git a/test/CodegenEnumTestCase.php b/test/CodegenEnumTestCase.php
index 9c2a4b93..be25bc81 100644
--- a/test/CodegenEnumTestCase.php
+++ b/test/CodegenEnumTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenEnumTestCase extends CodegenBaseTest {
 
   public function testDocblock() {
diff --git a/test/CodegenExpectedFile.php b/test/CodegenExpectedFile.php
index 07e6b3f4..2624c392 100644
--- a/test/CodegenExpectedFile.php
+++ b/test/CodegenExpectedFile.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 /**
  * The main purposes of this class are to:
  * 1) Serialize a Map<string,string> into a file.
diff --git a/test/CodegenFileTestCase.codegen b/test/CodegenFileTestCase.codegen
index 700d5143..2bc3ff29 100644
--- a/test/CodegenFileTestCase.codegen
+++ b/test/CodegenFileTestCase.codegen
@@ -8,6 +8,8 @@
  * Completely autogenerated!
  *
  * @-generated SignedSource<<38687075d6c73650c6f1db0ddc0289b1>>
+namespace Facebook/HackCodegen;
+
  */
 
 class AllAutogenerated {
diff --git a/test/CodegenFileTestCase.php b/test/CodegenFileTestCase.php
index 74c7a39b..91f5167b 100644
--- a/test/CodegenFileTestCase.php
+++ b/test/CodegenFileTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenFileTestCase extends CodegenBaseTest {
 
 
diff --git a/test/CodegenFunctionTestCase.codegen b/test/CodegenFunctionTestCase.codegen
index 4ddab6cd..30cc654a 100644
--- a/test/CodegenFunctionTestCase.codegen
+++ b/test/CodegenFunctionTestCase.codegen
@@ -8,6 +8,8 @@ async function genFoo() {
  * xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  * (Generated from EntTestSchema)
  */
+namespace Facebook/HackCodegen;
+
 function getName(): string {
   return $name;
 }
diff --git a/test/CodegenFunctionTestCase.php b/test/CodegenFunctionTestCase.php
index 85c6f3d0..abc36f80 100644
--- a/test/CodegenFunctionTestCase.php
+++ b/test/CodegenFunctionTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenFunctionTestCase extends CodegenBaseTest {
 
   public function testSimpleGetter() {
diff --git a/test/CodegenInterfaceTestCase.codegen b/test/CodegenInterfaceTestCase.codegen
index 21680f70..a0e8546f 100644
--- a/test/CodegenInterfaceTestCase.codegen
+++ b/test/CodegenInterfaceTestCase.codegen
@@ -8,6 +8,8 @@ interface IExtenderOfOne
   extends
     // Generated from Foo::Bar()
     IExtended {
+namespace Facebook/HackCodegen;
+
 }
 
 !@#$%codegentest:testExtendsInterfaces
diff --git a/test/CodegenInterfaceTestCase.php b/test/CodegenInterfaceTestCase.php
index 1b56ff35..45ae8588 100644
--- a/test/CodegenInterfaceTestCase.php
+++ b/test/CodegenInterfaceTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenInterfaceTestCase extends CodegenBaseTest {
 
 
diff --git a/test/CodegenMemberVarTestCase.codegen b/test/CodegenMemberVarTestCase.codegen
index e64e3259..5516e21a 100644
--- a/test/CodegenMemberVarTestCase.codegen
+++ b/test/CodegenMemberVarTestCase.codegen
@@ -8,6 +8,8 @@ private static $languages = array (
 
 !@#$%codegentest:testDocBlock
 // a comment
+namespace Facebook/HackCodegen;
+
 private $thingWithComment;
 
 !@#$%codegentest:testPublicStatic
diff --git a/test/CodegenMemberVarTestCase.php b/test/CodegenMemberVarTestCase.php
index 5b56d117..0f9d3e8f 100644
--- a/test/CodegenMemberVarTestCase.php
+++ b/test/CodegenMemberVarTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenMemberVarTestCase extends CodegenBaseTest {
 
   public function testSimple() {
diff --git a/test/CodegenMethodTestCase.codegen b/test/CodegenMethodTestCase.codegen
index 2ea18b65..261569da 100644
--- a/test/CodegenMethodTestCase.codegen
+++ b/test/CodegenMethodTestCase.codegen
@@ -8,6 +8,8 @@ public async function genFoo() {
 
 !@#$%codegentest:testConstructor
 public function __construct(string $name) {
+namespace Facebook/HackCodegen;
+
   $this->name = $name;
 }
 
diff --git a/test/CodegenMethodTestCase.php b/test/CodegenMethodTestCase.php
index e01501af..cb369e76 100644
--- a/test/CodegenMethodTestCase.php
+++ b/test/CodegenMethodTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenMethodTestCase extends CodegenBaseTest {
 
   public function testSimpleGetter() {
diff --git a/test/CodegenShapeTestCase.php b/test/CodegenShapeTestCase.php
index 80fd512f..98cdb150 100644
--- a/test/CodegenShapeTestCase.php
+++ b/test/CodegenShapeTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenShapeTestCase extends CodegenBaseTest {
 
 
diff --git a/test/CodegenSimpleTester.php b/test/CodegenSimpleTester.php
index e12a3664..52da4b12 100644
--- a/test/CodegenSimpleTester.php
+++ b/test/CodegenSimpleTester.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 require_once('CodegenExpectedFile.php');
 require_once('CodegenBaseTest.php');
 require_once('TestCodegenConfig.php');
diff --git a/test/CodegenTraitTestCase.codegen b/test/CodegenTraitTestCase.codegen
index ba25a904..46cde1a4 100644
--- a/test/CodegenTraitTestCase.codegen
+++ b/test/CodegenTraitTestCase.codegen
@@ -8,6 +8,8 @@ trait DemoInternal {
   require extends EntSchema;
   require implements IEntSchemaBase;
 
+namespace Facebook/HackCodegen;
+
   use EntProvisionalMode;
   // Generated from Whatever::Method()
   use WhateverTrait;
diff --git a/test/CodegenTraitTestCase.php b/test/CodegenTraitTestCase.php
index 4b2e0003..d87b3863 100644
--- a/test/CodegenTraitTestCase.php
+++ b/test/CodegenTraitTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenTraitTestCase extends CodegenBaseTest {
 
   public function testDocblock() {
diff --git a/test/CodegenTypeTestCase.codegen b/test/CodegenTypeTestCase.codegen
index 3de4884b..aaf993f3 100644
--- a/test/CodegenTypeTestCase.codegen
+++ b/test/CodegenTypeTestCase.codegen
@@ -8,6 +8,8 @@ type Point = shape(
   'y' => int,
 );
 
+namespace Facebook/HackCodegen;
+
 !@#$%codegentest:testType
 type Point = (int, int);
 
diff --git a/test/CodegenTypeTestCase.php b/test/CodegenTypeTestCase.php
index 717921a6..a9795be7 100644
--- a/test/CodegenTypeTestCase.php
+++ b/test/CodegenTypeTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class CodegenTypeTestCase extends CodegenBaseTest {
 
 
diff --git a/test/HackBuilderTestCase.codegen b/test/HackBuilderTestCase.codegen
index d9f5c5c4..ae23f2e1 100644
--- a/test/HackBuilderTestCase.codegen
+++ b/test/HackBuilderTestCase.codegen
@@ -8,6 +8,8 @@
 
 !@#$%codegentest:testAddSmartMultilineCall
 $foobarbaz_alphabetagama =
+namespace Facebook/HackCodegen;
+
   $this->callSomeThingReallyLongNameReallyReallyLongName(
   $someSmallParameter,
   $foobarbaz_alphabetagama + $foobarbaz_alphabetagamaa +
diff --git a/test/HackBuilderTestCase.php b/test/HackBuilderTestCase.php
index 1e557254..770014f6 100644
--- a/test/HackBuilderTestCase.php
+++ b/test/HackBuilderTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class HackBuilderTestCase extends CodegenBaseTest {
 
   public function testIfBlock() {
diff --git a/test/RefactorCodegenTestCase.codegen b/test/RefactorCodegenTestCase.codegen
index 4179d23e..c49ec029 100644
--- a/test/RefactorCodegenTestCase.codegen
+++ b/test/RefactorCodegenTestCase.codegen
@@ -8,6 +8,8 @@
  *
  * @-partially-generated SignedSource<<e771f47c7d37d21e6f2ec80ea8390b39>>
  */
+namespace Facebook/HackCodegen;
+
 
 class NewClass {
 
diff --git a/test/RefactorCodegenTestCase.php b/test/RefactorCodegenTestCase.php
index 02cb90b7..3fe3e03a 100644
--- a/test/RefactorCodegenTestCase.php
+++ b/test/RefactorCodegenTestCase.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class RefactorCodegenTestCase extends CodegenBaseTest {
 
   /**
diff --git a/test/TestCodegenConfig.php b/test/TestCodegenConfig.php
index 47d4dddb..2ae19e14 100644
--- a/test/TestCodegenConfig.php
+++ b/test/TestCodegenConfig.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 final class TestCodegenConfig implements IHackCodegenConfig {
 
   <<__Memoize>>
diff --git a/test/run_tests.php b/test/run_tests.php
index 6b8a9189..59dbbaa8 100644
--- a/test/run_tests.php
+++ b/test/run_tests.php
@@ -8,6 +8,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
+namespace Facebook/HackCodegen;
+
 require_once('vendor/autoload.php');
 require_once('CodegenSimpleTester.php');
 $success = CodegenSimpleTester::run();