For simplicity don't pass flags to dependencies.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e4f06f1..22c9d4b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -61,7 +61,7 @@
   set(FUZZING_FLAGS "-fsanitize-coverage=${FUZZING_FLAGS}")
 endif()
 
-set(EXTRA_FLAGS "-fno-exceptions")
+set(EXTRA_FLAGS "-fno-exceptions -Werror -Wall")
 if (LIB_PROTO_MUTATOR_WITH_ASAN)
   if (LIB_PROTO_MUTATOR_HAS_SANITIZE_ADDRESS)
     set(EXTRA_FLAGS "${EXTRA_FLAGS} -fsanitize=address")