diff --git a/.bazelrc b/.bazelrc
index a74f3894..2cb48988 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -20,8 +20,8 @@ build --action_env=CXX=clang++
 
 # Use the C++17 standard.
 build --cxxopt=-std=c++17
-# ...But disable warnings about C++20 extensions.
-build --cxxopt=-Wno-c++20-extensions
+# Report error on C++20 extensions.
+build --cxxopt=-Werror-c++20-extensions
 # Required by the cc_fuzztest_grammar_library rule, which uses the
 # "exec configuration" (https://bazel.build/reference/be/general#cross-compilation-considerations).
 # The --cxxopt flag does not apply to the exec configuration, only the