diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index db3e21ff135..c7e1e325c8e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -252,7 +252,7 @@ jobs:
         run: |
           pip install -r dev_tools/requirements/deps/protos.txt
       - name: Build protos
-        run: check/build-changed-protos
+        run: check/protos-up-to-date
   coverage:
     name: Coverage check
     runs-on: ubuntu-20.04
diff --git a/check/build-changed-protos b/check/build-changed-protos
deleted file mode 100755
index df58599498b..00000000000
--- a/check/build-changed-protos
+++ /dev/null
@@ -1,74 +0,0 @@
-#!/usr/bin/env bash
-
-################################################################################
-# Runs bazel build for proto files in cirq/google/api/* that have changed.
-#
-# If any BUILD file for the proto has changed, all targets in that BUILD
-# file will be built.
-#
-# Usage:
-#     check/build-changed-protos [BASE_REVISION]
-#
-# You can specify a base git revision to compare against (i.e. to use when
-# determining whether or not a line is considered to have "changed"). For
-# example, you can compare against 'origin/main' or 'HEAD~1'.
-#
-# If you don't specify a base revision, the following defaults will be tried, in
-# order, until one exists:
-#
-#     1. upstream/main
-#     2. origin/main
-#     3. main
-#
-# If none exists, the script fails.
-#
-# See build-protos for building all protos.
-################################################################################
-
-# Get the working directory to the repo root.
-thisdir="$(dirname "${BASH_SOURCE[0]}")" || exit $?
-topdir="$(git -C "${thisdir}" rev-parse --show-toplevel)" || exit $?
-cd "${topdir}" || exit $?
-
-# Figure out which revision to compare against.
-if [ -n "$1" ] && [[ $1 != -* ]]; then
-    if ! git rev-parse --verify --quiet --no-revs "$1^{commit}"; then
-        echo -e "\033[31mNo revision '$1'.\033[0m" >&2
-        exit 1
-    fi
-    rev=$1
-elif [ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]; then
-    rev=upstream/main
-elif [ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]; then
-    rev=origin/main
-elif [ "$(git cat-file -t main 2> /dev/null)" == "commit" ]; then
-    rev=main
-else
-    echo -e "\033[31mNo default revision found to compare against. Argument #1 must be what to diff against (e.g. 'origin/main' or 'HEAD~1').\033[0m" >&2
-    exit 1
-fi
-base="$(git merge-base "${rev}" HEAD)"
-if [ "$(git rev-parse "${rev}")" == "${base}" ]; then
-    echo -e "Comparing against revision '${rev}'." >&2
-else
-    echo -e "Comparing against revision '${rev}' (merge base ${base})." >&2
-    rev="${base}"
-fi
-
-# All the protos.
-echo "Building protos in $PWD"
-
-dev_tools/build-protos.sh
-
-# Filenames with spaces will be ugly (each part will be listed separately)
-# but the error logic will still work.
-uncommitted=$(git status --porcelain 2>/dev/null | grep -E "^[?][?] cirq-google" | cut -d " " -f 3)
-
-if [[ -n "$uncommitted" ]]; then
-    echo -e "\033[31mERROR: Uncommitted generated files found! Please generate and commit these files using dev_tools/build-protos.sh:\033[0m"
-    for generated in $uncommitted
-    do
-        echo -e "\033[31m   ${generated}\033[0m"
-    done
-    exit 1
-fi
diff --git a/check/protos-up-to-date b/check/protos-up-to-date
new file mode 100755
index 00000000000..5543533ed13
--- /dev/null
+++ b/check/protos-up-to-date
@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+################################################################################
+# Verifies that Python files generated from protobuf definitions are up to date.
+#
+# See dev_tools/build-protos.sh for building all protos.
+################################################################################
+
+# Get the working directory to the repo root.
+thisdir="$(dirname "${BASH_SOURCE[0]}")" || exit $?
+topdir="$(git -C "${thisdir}" rev-parse --show-toplevel)" || exit $?
+cd "${topdir}" || exit $?
+
+git_status="$(git status --short)"
+if [[ -n "${git_status}" ]]; then
+    echo "$0 requires a pristine worktree, but 'git status' shows"
+    echo "some changes or untracked files."
+    echo
+    echo "Please commit or clean these up to try again."
+    exit 2
+fi
+
+echo "Removing generated Python files.  If not restored by this script use"
+echo 'git restore "*_pb2.py*"    to recover them back.'
+echo
+
+git rm --quiet "cirq-google/*_pb2.py*"
+# restore deleted files in git index
+git reset --quiet
+
+echo "Building protos in $PWD"
+echo
+
+dev_tools/build-protos.sh
+
+git_status="$(git status --short)"
+
+if [[ -n "${git_status}" ]]; then
+    echo
+    echo -e "\033[31mERROR: dev_tools/build-protos.sh changed generated files!\033[0m"
+    echo -e "\033[31mPlease update and commit these files using dev_tools/build-protos.sh\033[0m"
+    echo
+    echo "Output of 'git status' (note there may be untracked new files or deleted old ones):"
+    echo
+    git status
+    exit 1
+fi