diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8fa142b..892382e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -56,8 +56,14 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # Self-hosted act runners run as root in a container that has no sudo,
+      # while GitHub-hosted runners need it. Pick whichever exists.
       - name: Install protoc
-        run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
+        run: |
+          SUDO=""
+          if [ "$(id -u)" -ne 0 ]; then SUDO="sudo"; fi
+          $SUDO apt-get update
+          $SUDO apt-get install -y protobuf-compiler
 
       - uses: dtolnay/rust-toolchain@stable
         with: