diff --git a/tools/grpc_generator/poetry.lock b/tools/grpc_generator/poetry.lock
index 2e38f84b..820c8e6d 100644
--- a/tools/grpc_generator/poetry.lock
+++ b/tools/grpc_generator/poetry.lock
@@ -1229,6 +1229,13 @@ optional = false
 python-versions = ">=3.8"
 groups = ["lint"]
 files = [
+    {file = "PyYAML-6.0.3-cp38-cp38-macosx_10_13_x86_64.whl", hash = "sha256:c2514fceb77bc5e7a2f7adfaa1feb2fb311607c9cb518dbc378688ec73d8292f"},
+    {file = "PyYAML-6.0.3-cp38-cp38-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:9c57bb8c96f6d1808c030b1687b9b5fb476abaa47f0db9c0101f5e9f394e97f4"},
+    {file = "PyYAML-6.0.3-cp38-cp38-manylinux2014_s390x.manylinux_2_17_s390x.manylinux_2_28_s390x.whl", hash = "sha256:efd7b85f94a6f21e4932043973a7ba2613b059c4a000551892ac9f1d11f5baf3"},
+    {file = "PyYAML-6.0.3-cp38-cp38-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:22ba7cfcad58ef3ecddc7ed1db3409af68d023b7f940da23c6c2a1890976eda6"},
+    {file = "PyYAML-6.0.3-cp38-cp38-musllinux_1_2_x86_64.whl", hash = "sha256:6344df0d5755a2c9a276d4473ae6b90647e216ab4757f8426893b5dd2ac3f369"},
+    {file = "PyYAML-6.0.3-cp38-cp38-win32.whl", hash = "sha256:3ff07ec89bae51176c0549bc4c63aa6202991da2d9a6129d7aef7f1407d3f295"},
+    {file = "PyYAML-6.0.3-cp38-cp38-win_amd64.whl", hash = "sha256:5cf4e27da7e3fbed4d6c3d8e797387aaad68102272f8f9752883bc32d61cb87b"},
     {file = "pyyaml-6.0.3-cp310-cp310-macosx_10_13_x86_64.whl", hash = "sha256:214ed4befebe12df36bcc8bc2b64b396ca31be9304b8f59e25c11cf94a4c033b"},
     {file = "pyyaml-6.0.3-cp310-cp310-macosx_11_0_arm64.whl", hash = "sha256:02ea2dfa234451bbb8772601d7b8e426c2bfa197136796224e50e35a78777956"},
     {file = "pyyaml-6.0.3-cp310-cp310-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:b30236e45cf30d2b8e7b3e85881719e98507abed1011bf463a8fa23e9c3e98a8"},
@@ -1454,4 +1461,4 @@ markers = {test = "python_version == \"3.10\""}
 [metadata]
 lock-version = "2.1"
 python-versions = ">=3.10,<4.0"
-content-hash = "e6ce885003137f1d1025f2809817a0fb3762344ad835cfe10e4c1b275c7efe7b"
+content-hash = "9af2a3b0e3da078ab89a94bba594f8c3df475b65a4808dd9bfeaf39bcf14d36e"
diff --git a/tools/grpc_generator/pyproject.toml b/tools/grpc_generator/pyproject.toml
index ae8fc03c..46ea285f 100644
--- a/tools/grpc_generator/pyproject.toml
+++ b/tools/grpc_generator/pyproject.toml
@@ -28,7 +28,8 @@ grpcio-tools = [
   { version = "1.67.0", python = ">=3.13,<3.14" },
   { version = "1.75.1", python = "^3.14" },
 ]
-mypy-protobuf = ">=3.6"
+# mypy-protobuf 3.6 is the last version that supports protobuf v4.
+mypy-protobuf = ">=3.6,<3.7"
 
 [tool.poetry.group.lint.dependencies]
 bandit = { version = ">=1.7", extras = ["toml"] }