diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6f2fa19db..a36189576 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -64,8 +64,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # windows-latest disabled: see #<issue> — record the reason, not just the comment
-        os: [ ubuntu-latest, macos-latest ]
+        os: [ ubuntu-latest, windows-latest, macos-latest ]
     steps:
       - uses: actions/checkout@v5
         with:
diff --git a/.mvn/jvm.config b/.mvn/jvm.config
new file mode 100644
index 000000000..7fecadb38
--- /dev/null
+++ b/.mvn/jvm.config
@@ -0,0 +1 @@
+-Dfile.encoding=UTF-8
diff --git a/pom.xml b/pom.xml
index 212e1fe8f..1f28ee1d2 100644
--- a/pom.xml
+++ b/pom.xml
@@ -426,6 +426,11 @@
                         <goals>
                             <goal>jjtree-javacc</goal>
                         </goals>
+                        <!--
+                            GRAMMAR_ENCODING governs reading only: JJTree writes the intermediate
+                            .jj with the JVM default charset, which mangles the grammar's non-ASCII
+                            character classes unless file.encoding is UTF-8 (see .mvn/jvm.config).
+                        -->
                         <configuration>
                             <javaccCmdLineArgs>
                                 <arg>-CODE_GENERATOR:"Java"</arg>
@@ -564,11 +569,13 @@
                         @{jacocoArgLine} is resolved late, after jacoco:prepare-agent has run.
                         Without it the JaCoCo agent would be dropped and coverage reports empty.
                     -->
+                    <!-- Forked test JVMs do not inherit .mvn/jvm.config, so pin the encoding here too. -->
                     <argLine>
                         @{jacocoArgLine}
                         --add-opens=java.base/java.lang=ALL-UNNAMED
                         --add-opens=java.base/java.util=ALL-UNNAMED
                         -Xmx2G -Xms800m -Xss4m
+                        -Dfile.encoding=UTF-8
                     </argLine>
                 </configuration>
             </plugin>