diff --git a/.bazeliskrc b/.bazeliskrc
index e920830..bd4a535 100644
--- a/.bazeliskrc
+++ b/.bazeliskrc
@@ -1 +1 @@
-USE_BAZEL_VERSION=7.7.0
+USE_BAZEL_VERSION=5.4.1
diff --git a/.bazelrc b/.bazelrc
index 7cedb34..7a9655a 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -1,16 +1,8 @@
-# Disable Bazel modules (for now).
-common --enable_bzlmod=false
-
-build --cxxopt='-std=c++17'
-build --host_cxxopt='-std=c++17'
-
 # Use a remote build cache that's world-readable. Don't write unless told otherwise.
+
 build --remote_cache=https://storage.googleapis.com/reboot-dev-bazel-remote-cache-reboot-us
 build --remote_upload_local_results=false
 
 # Print full test logs for failed tests.
-test --test_output=errors
 
-# To debug errors using the remote cache we need the `--verbose_failures` flag to
-# get any useful information whatsoever.
-build --verbose_failures
+test --test_output=errors
diff --git a/WORKSPACE.bazel b/WORKSPACE.bazel
index 3790e29..d73f3a8 100644
--- a/WORKSPACE.bazel
+++ b/WORKSPACE.bazel
@@ -2,7 +2,7 @@ workspace(name = "com_github_reboot_dev_pyprotoc_plugin")
 
 load("//bazel:repos.bzl", "repos")
 
-repos()
+repos(external = False)
 
 load("//bazel:py_toolchains.bzl", "py_toolchains")
 
diff --git a/bazel/deps.bzl b/bazel/deps.bzl
index 0cbe689..510ca54 100644
--- a/bazel/deps.bzl
+++ b/bazel/deps.bzl
@@ -3,7 +3,7 @@
 load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
 load("@pyprotoc_plugin_pypi//:requirements.bzl", pypi_deps = "install_deps")
 
-def deps():
+def deps(repo_mapping = {}):
     protobuf_deps()
 
-    pypi_deps()
+    pypi_deps(repo_mapping = repo_mapping)
diff --git a/bazel/py_toolchains.bzl b/bazel/py_toolchains.bzl
index a80795b..e300d5f 100644
--- a/bazel/py_toolchains.bzl
+++ b/bazel/py_toolchains.bzl
@@ -2,10 +2,11 @@
 
 load("@rules_python//python:repositories.bzl", "py_repositories", "python_register_toolchains")
 
-def py_toolchains():
+def py_toolchains(repo_mapping = {}):
     py_repositories()
 
     python_register_toolchains(
         name = "python3_10_12",
         python_version = "3.10.12",
+        repo_mapping = repo_mapping,
     )
diff --git a/bazel/pypi_repos.bzl b/bazel/pypi_repos.bzl
index ebf8407..0647888 100644
--- a/bazel/pypi_repos.bzl
+++ b/bazel/pypi_repos.bzl
@@ -3,11 +3,12 @@ should be installed later in WORKSPACE file to be accessible.
 `pip_parse` takes a `requirements_lock` file as input, which is
 generated by the `bazel run :requirements.update` command."""
 
+load("@python3_10_12//:defs.bzl", "interpreter")
 load("@rules_python//python:pip.bzl", "pip_parse")
 
 def pypi_repos():
     pip_parse(
         name = "pyprotoc_plugin_pypi",
-        python_interpreter_target = "@python3_10_12_host//:python",
+        python_interpreter_target = interpreter,
         requirements_lock = "@com_github_reboot_dev_pyprotoc_plugin//:requirements_lock.txt",
     )
diff --git a/bazel/repos.bzl b/bazel/repos.bzl
index b10f677..a5cf218 100644
--- a/bazel/repos.bzl
+++ b/bazel/repos.bzl
@@ -9,26 +9,43 @@
 # instructions at https://github.com/reboot-dev/pyprotoc-plugin.
 ########################################################################
 
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
-load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 
-def repos():
-    """Adds repositories/archives needed by pyprotoc-plugin."""
+def repos(external = True, repo_mapping = {}):
+    """Adds repositories/archives needed by pyprotoc-plugin
 
-    maybe(
-        http_archive,
+    Args:
+          external: whether or not we're invoking this function as though
+            though we're an external dependency
+          repo_mapping: passed through to all other functions that expect/use
+            repo_mapping, e.g., 'git_repository'
+    """
+    http_archive(
         name = "rules_python",
-        sha256 = "4f7e2aa1eb9aa722d96498f5ef514f426c1f55161c3c9ae628c857a7128ceb07",
-        strip_prefix = "rules_python-1.0.0",
-        url = "https://github.com/bazelbuild/rules_python/releases/download/1.0.0/rules_python-1.0.0.tar.gz",
+        sha256 = "9acc0944c94adb23fba1c9988b48768b1bacc6583b52a2586895c5b7491e2e31",
+        strip_prefix = "rules_python-0.27.0",
+        url = "https://github.com/bazelbuild/rules_python/releases/download/0.27.0/rules_python-0.27.0.tar.gz",
+        repo_mapping = repo_mapping,
     )
 
-    maybe(
-        http_archive,
-        name = "com_google_protobuf",
-        sha256 = "955ef3235be41120db4d367be81efe6891c9544b3a71194d80c3055865b26e09",
-        strip_prefix = "protobuf-29.5",
-        urls = [
-            "https://github.com/protocolbuffers/protobuf/archive/v29.5.tar.gz",
-        ],
-    )
+    if "com_google_protobuf" not in native.existing_rules():
+        git_repository(
+            name = "com_google_protobuf",
+            remote = "https://github.com/protocolbuffers/protobuf",
+            # Release v3.19.4.
+            # TODO(codingcanuck): Update to a newer release after
+            # https://github.com/protocolbuffers/protobuf/issues/9688 is fixed.
+            commit = "22d0e265de7d2b3d2e9a00d071313502e7d4cccf",
+            shallow_since = "1643340956 -0800",
+            repo_mapping = repo_mapping,
+        )
+
+    if external and "com_github_reboot_dev_pyprotoc_plugin" not in native.existing_rules():
+        git_repository(
+            name = "com_github_reboot_dev_pyprotoc_plugin",
+            remote = "https://github.com/reboot-dev/pyprotoc-plugin",
+            commit = "9f7a281670f03b77140c4437ac2a56b86f978af6",
+            shallow_since = "1649038239 +0000",
+            repo_mapping = repo_mapping,
+        )
diff --git a/requirements.in b/requirements.in
index 7423a20..9fb21af 100644
--- a/requirements.in
+++ b/requirements.in
@@ -1,2 +1,2 @@
 Jinja2>=3
-protobuf>= 5.29.5
+protobuf>=3
diff --git a/requirements_lock.txt b/requirements_lock.txt
index 36a6a0f..63b8c40 100644
--- a/requirements_lock.txt
+++ b/requirements_lock.txt
@@ -70,14 +70,16 @@ markupsafe==2.1.3 \
     --hash=sha256:fec21693218efe39aa7f8599346e90c705afa52c5b31ae019b2e57e8f6542bb2 \
     --hash=sha256:ffcc3f7c66b5f5b7931a5aa68fc9cecc51e685ef90282f4a82f0f5e9b704ad11
     # via jinja2
-protobuf==6.32.1 \
-    --hash=sha256:2601b779fc7d32a866c6b4404f9d42a3f67c5b9f3f15b4db3cccabe06b95c346 \
-    --hash=sha256:2f5b80a49e1eb7b86d85fcd23fe92df154b9730a725c3b38c4e43b9d77018bf4 \
-    --hash=sha256:68ff170bac18c8178f130d1ccb94700cf72852298e016a2443bdb9502279e5f1 \
-    --hash=sha256:a8a32a84bc9f2aad712041b8b366190f71dde248926da517bde9e832e4412085 \
-    --hash=sha256:b00a7d8c25fa471f16bc8153d0e53d6c9e827f0953f3c09aaa4331c718cae5e1 \
-    --hash=sha256:b1864818300c297265c83a4982fd3169f97122c299f56a56e2445c3698d34710 \
-    --hash=sha256:d0975d0b2f3e6957111aa3935d08a0eb7e006b1505d825f862a1fffc8348e122 \
-    --hash=sha256:d8c7e6eb619ffdf105ee4ab76af5a68b60a9d0f66da3ea12d1640e6d8dab7281 \
-    --hash=sha256:ee2469e4a021474ab9baafea6cd070e5bf27c7d29433504ddea1a4ee5850f68d
+protobuf==4.25.1 \
+    --hash=sha256:0bf384e75b92c42830c0a679b0cd4d6e2b36ae0cf3dbb1e1dfdda48a244f4bcd \
+    --hash=sha256:0f881b589ff449bf0b931a711926e9ddaad3b35089cc039ce1af50b21a4ae8cb \
+    --hash=sha256:1484f9e692091450e7edf418c939e15bfc8fc68856e36ce399aed6889dae8bb0 \
+    --hash=sha256:193f50a6ab78a970c9b4f148e7c750cfde64f59815e86f686c22e26b4fe01ce7 \
+    --hash=sha256:3497c1af9f2526962f09329fd61a36566305e6c72da2590ae0d7d1322818843b \
+    --hash=sha256:57d65074b4f5baa4ab5da1605c02be90ac20c8b40fb137d6a8df9f416b0d0ce2 \
+    --hash=sha256:8bdbeaddaac52d15c6dce38c71b03038ef7772b977847eb6d374fc86636fa510 \
+    --hash=sha256:a19731d5e83ae4737bb2a089605e636077ac001d18781b3cf489b9546c7c80d6 \
+    --hash=sha256:abc0525ae2689a8000837729eef7883b9391cd6aa7950249dcf5a4ede230d5dd \
+    --hash=sha256:becc576b7e6b553d22cbdf418686ee4daa443d7217999125c045ad56322dda10 \
+    --hash=sha256:ca37bf6a6d0046272c152eea90d2e4ef34593aaa32e8873fc14c16440f22d4b7
     # via -r requirements.in
diff --git a/rules.bzl b/rules.bzl
index 741fec3..e3cde4a 100644
--- a/rules.bzl
+++ b/rules.bzl
@@ -1,6 +1,6 @@
 """Defines rules to create pyprotoc-based bazel rules."""
 
-load("@com_google_protobuf//bazel/common:proto_info.bzl", "ProtoInfo")
+load("@rules_proto//proto:defs.bzl", "ProtoInfo")
 
 def _get_proto_sources(context):
     proto_files = [
diff --git a/tests/cpp/BUILD.bazel b/tests/cpp/BUILD.bazel
index 9913a99..8a20e3f 100644
--- a/tests/cpp/BUILD.bazel
+++ b/tests/cpp/BUILD.bazel
@@ -1,6 +1,5 @@
-load("@com_google_protobuf//bazel:cc_proto_library.bzl", "cc_proto_library")
-load("@com_google_protobuf//bazel:proto_library.bzl", "proto_library")
-load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
+load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_proto_library")
+load("@rules_proto//proto:defs.bzl", "proto_library")
 load("@rules_python//python:defs.bzl", "py_binary")
 load(":cpp_rule.bzl", "cc_generate_library")
 
@@ -55,9 +54,8 @@ cc_library(
     ],
 )
 
-cc_test(
+cc_binary(
     name = "cc_test",
-    size = "small",
     srcs = ["cc_generated_test.cc"],
     deps = [
         ":cc_library_generated",
diff --git a/tests/python/BUILD.bazel b/tests/python/BUILD.bazel
index eac5756..f6d17fd 100644
--- a/tests/python/BUILD.bazel
+++ b/tests/python/BUILD.bazel
@@ -1,11 +1,10 @@
-load("@com_google_protobuf//bazel:proto_library.bzl", "proto_library")
-load("@com_google_protobuf//bazel:py_proto_library.bzl", "py_proto_library")
+load("@com_google_protobuf//:protobuf.bzl", "py_proto_library")
+load("@rules_proto//proto:defs.bzl", "proto_library")
 load("@rules_python//python:defs.bzl", "py_binary", "py_library", "py_test")
 load(":sample_rule.bzl", "py_sample_library")
 
 py_test(
     name = "library_tests",
-    size = "small",
     srcs = [
         "library_tests.py",
     ],
@@ -31,7 +30,7 @@ proto_library(
 
 py_proto_library(
     name = "sample_messages_py_proto",
-    deps = [":sample_messages_proto"],
+    srcs = ["sample_messages.proto"],
 )
 
 proto_library(
@@ -42,7 +41,8 @@ proto_library(
 
 py_proto_library(
     name = "sample_service_py_proto",
-    deps = [":sample_messages_proto"],
+    srcs = ["sample_service.proto"],
+    deps = [":sample_messages_py_proto"],
 )
 
 py_sample_library(
@@ -62,7 +62,6 @@ py_library(
 
 py_test(
     name = "sample_generated_library_test",
-    size = "small",
     srcs = [
         "sample_generated_library_test.py",
     ],