diff --git a/CHANGELOG.md b/CHANGELOG.md
index 716ce9d9..5d32db83 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 4.0.3
+
+* Widen `package:protobuf` constraint to allow version 4.0.0.
+
 ## 4.0.2
 
 * Internal optimization to client code.
diff --git a/example/googleapis/pubspec.yaml b/example/googleapis/pubspec.yaml
index b2c12db6..139bf224 100644
--- a/example/googleapis/pubspec.yaml
+++ b/example/googleapis/pubspec.yaml
@@ -3,14 +3,14 @@ description: Dart gRPC client sample for Google APIs
 publish_to: none
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   async: ^2.2.0
   fixnum:
   grpc:
     path: ../../
-  protobuf: ^3.0.0
+  protobuf: ">=3.0.0 <5.0.0"
 
 dev_dependencies:
   lints: ^2.0.0
diff --git a/example/grpc-web/pubspec.yaml b/example/grpc-web/pubspec.yaml
index 4719ec17..f48411e7 100644
--- a/example/grpc-web/pubspec.yaml
+++ b/example/grpc-web/pubspec.yaml
@@ -8,7 +8,7 @@ environment:
 dependencies:
   grpc:
     path: ../../
-  protobuf: ^3.0.0
+  protobuf: ">=3.0.0 <5.0.0"
   web: ^1.1.0
 
 dev_dependencies:
diff --git a/example/helloworld/pubspec.yaml b/example/helloworld/pubspec.yaml
index 33431c50..7e5da048 100644
--- a/example/helloworld/pubspec.yaml
+++ b/example/helloworld/pubspec.yaml
@@ -3,13 +3,13 @@ description: Dart gRPC sample client and server.
 publish_to: none
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   async: ^2.2.0
   grpc:
     path: ../../
-  protobuf: ^3.0.0
+  protobuf: ">=3.0.0 <5.0.0"
 
 dev_dependencies:
   lints: ^2.0.0
diff --git a/example/metadata/pubspec.yaml b/example/metadata/pubspec.yaml
index 61e0dc63..1582aaed 100644
--- a/example/metadata/pubspec.yaml
+++ b/example/metadata/pubspec.yaml
@@ -3,13 +3,13 @@ description: Dart gRPC sample client and server.
 publish_to: none
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   async: ^2.2.0
   grpc:
     path: ../../
-  protobuf: ^3.0.0
+  protobuf: ">=3.0.0 <5.0.0"
 
 dev_dependencies:
   lints: ^2.0.0
diff --git a/example/route_guide/pubspec.yaml b/example/route_guide/pubspec.yaml
index 164885f3..7f6550c1 100644
--- a/example/route_guide/pubspec.yaml
+++ b/example/route_guide/pubspec.yaml
@@ -3,13 +3,13 @@ description: Dart gRPC sample client and server.
 publish_to: none
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   async: ^2.2.0
   grpc:
     path: ../../
-  protobuf: ^3.0.0
+  protobuf: ">=3.0.0 <5.0.0"
   collection: ^1.15.0-nullsafety.4
 
 dev_dependencies:
diff --git a/interop/pubspec.yaml b/interop/pubspec.yaml
index f4038fae..b5546726 100644
--- a/interop/pubspec.yaml
+++ b/interop/pubspec.yaml
@@ -11,7 +11,7 @@ dependencies:
   collection: ^1.14.11
   grpc:
     path: ../
-  protobuf: ^3.0.0
+  protobuf: ">=3.0.0 <5.0.0"
 
 dev_dependencies:
   test: ^1.16.0
diff --git a/pubspec.yaml b/pubspec.yaml
index 75f82b1a..e08d9c6d 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: grpc
-version: 4.0.2
+version: 4.0.3
 description: Dart implementation of gRPC, a high performance, open-source universal RPC framework.
 repository: https://github.com/grpc/grpc-dart
 
@@ -17,9 +17,9 @@ dependencies:
   fixnum: ^1.0.0
   googleapis_auth: ^1.1.0
   meta: ^1.3.0
-  http: '>=0.13.0 <2.0.0'
+  http: ">=0.13.0 <2.0.0"
   http2: ^2.2.0
-  protobuf: '>=2.0.0 <4.0.0'
+  protobuf: ">=2.0.0 <5.0.0"
   clock: ^1.1.1
   web: ^1.1.0