diff --git a/ci/config.mk.clang-12.sed b/ci/config.mk.clang-12.sed
index 810b723..6b59a18 100644
--- a/ci/config.mk.clang-12.sed
+++ b/ci/config.mk.clang-12.sed
@@ -1,3 +1,3 @@
 # Clang 12 (or Apple clang 13) and later makes a warning '-Wcompound-token-split-by-macro' enable by default.
-/^PERL_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=compound-token-split-by-macro/
+/^PERL_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=compound-token-split-by-macro -Wno-compound-token-split-by-macro/
 /^RUBY_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=compound-token-split-by-macro/
diff --git a/ci/config.mk.sed b/ci/config.mk.sed
index 06b6f73..d888901 100644
--- a/ci/config.mk.sed
+++ b/ci/config.mk.sed
@@ -1,3 +1,3 @@
-/^CFLAGS[[:blank:]]*=/s/$/ -Wall -Wextra -Wshadow -Werror -Wno-deprecated-declarations/
+/^CFLAGS[[:blank:]]*=/s/$/ -Wall -Wextra -Wshadow -Wstrict-prototypes -Wmissing-prototypes -Werror -Wno-deprecated-declarations/
 /^PERL_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=unused-function -Wno-shadow/
-/^RUBY_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=unused-parameter/
+/^RUBY_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=unused-parameter -Wno-strict-prototypes/