diff --git a/test/test_service.proto b/test/test_service.proto
index 9ba3a686..5d3d8918 100644
--- a/test/test_service.proto
+++ b/test/test_service.proto
@@ -27,7 +27,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-syntax = "proto3";
+syntax = "proto2";
 
 message Request {
   optional bool error = 1;