diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index becf99029..e553d062f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -19,6 +19,7 @@ jobs:
         # ubuntu-22.04 uses OpenSSL 3.0, ubuntu-20.04 uses OpenSSL 1.1.1
         os: [ ubuntu-22.04, ubuntu-20.04, macos-latest, windows-latest ]
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
+        fail_by_warn: [ true ]
         exclude:
           # uses non-standard MSYS2 OpenSSL 3 package
           - { os: windows-latest, ruby: head }
@@ -47,6 +48,10 @@ jobs:
         run:  echo "MAKEFLAGS=V=1" >> $GITHUB_ENV
         if: runner.os == 'Linux' || runner.os == 'macOS'
 
+      - name: set flags to fail by the compiler warnings.
+        run:  echo "RUBY_OPENSSL_EXTCFLAGS=-Werror" >> $GITHUB_ENV
+        if: matrix.fail_by_warn
+
       - name: compile
         run:  rake compile -- --enable-debug
 
@@ -75,6 +80,7 @@ jobs:
           - libressl-3.5.3
           - libressl-3.6.1
           - libressl-3.7.0 # Development release
+        fail_by_warn: [ true ]
         fips_enabled: [ false ]
         include:
           - { os: ubuntu-latest, ruby: "3.0", openssl: openssl-3.0.8, fips_enabled: true, append_configure: 'enable-fips', name_extra: 'fips' }
@@ -138,6 +144,10 @@ jobs:
         run:  echo "MAKEFLAGS=V=1" >> $GITHUB_ENV
         if: runner.os == 'Linux' || runner.os == 'macOS'
 
+      - name: set flags to fail by the compiler warnings.
+        run:  echo "RUBY_OPENSSL_EXTCFLAGS=-Werror" >> $GITHUB_ENV
+        if: matrix.fail_by_warn
+
       - name: compile
         run:  rake compile -- --enable-debug --with-openssl-dir=$HOME/.openssl/${{ matrix.openssl }}