diff --git a/php/src/GPBMetadata/Google/Protobuf/Any.php b/php/src/GPBMetadata/Google/Protobuf/Any.php
index c9a2952010..c6f457060c 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Any.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Any.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Any
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Api.php b/php/src/GPBMetadata/Google/Protobuf/Api.php
index 83e2748e4c..816b1c2b6a 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Api.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Api.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Api
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Duration.php b/php/src/GPBMetadata/Google/Protobuf/Duration.php
index 29e02a8451..947b20c3b4 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Duration.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Duration.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Duration
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/FieldMask.php b/php/src/GPBMetadata/Google/Protobuf/FieldMask.php
index 394e41043a..260247c67a 100644
--- a/php/src/GPBMetadata/Google/Protobuf/FieldMask.php
+++ b/php/src/GPBMetadata/Google/Protobuf/FieldMask.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class FieldMask
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/GPBEmpty.php b/php/src/GPBMetadata/Google/Protobuf/GPBEmpty.php
index 2842d0e992..8370d64f21 100644
--- a/php/src/GPBMetadata/Google/Protobuf/GPBEmpty.php
+++ b/php/src/GPBMetadata/Google/Protobuf/GPBEmpty.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class GPBEmpty
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Internal/Descriptor.php b/php/src/GPBMetadata/Google/Protobuf/Internal/Descriptor.php
index 8b1d955d1e..cf04ed95cc 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Internal/Descriptor.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Internal/Descriptor.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf\Internal;
 
 class Descriptor
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/SourceContext.php b/php/src/GPBMetadata/Google/Protobuf/SourceContext.php
index 8d1566c05a..649691068f 100644
--- a/php/src/GPBMetadata/Google/Protobuf/SourceContext.php
+++ b/php/src/GPBMetadata/Google/Protobuf/SourceContext.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class SourceContext
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Struct.php b/php/src/GPBMetadata/Google/Protobuf/Struct.php
index 6fad5d9a83..2c1169ba20 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Struct.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Struct.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Struct
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Timestamp.php b/php/src/GPBMetadata/Google/Protobuf/Timestamp.php
index fd4eaacc9d..e1fdb4f8d8 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Timestamp.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Timestamp.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Timestamp
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Type.php b/php/src/GPBMetadata/Google/Protobuf/Type.php
index 6bec20ded3..5e93d4cb54 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Type.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Type.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Type
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {
diff --git a/php/src/GPBMetadata/Google/Protobuf/Wrappers.php b/php/src/GPBMetadata/Google/Protobuf/Wrappers.php
index 49f84252b6..9b9eeaea9b 100644
--- a/php/src/GPBMetadata/Google/Protobuf/Wrappers.php
+++ b/php/src/GPBMetadata/Google/Protobuf/Wrappers.php
@@ -7,9 +7,9 @@ namespace GPBMetadata\Google\Protobuf;
 
 class Wrappers
 {
-    public static $is_initialized = false;
+    public static bool $is_initialized = false;
 
-    public static function initOnce() {
+    public static function initOnce(): void {
         $pool = \Google\Protobuf\Internal\DescriptorPool::getGeneratedPool();
 
         if (static::$is_initialized == true) {