diff --git a/src/bin/mathml2text.rs b/src/bin/mathml2text.rs
index ff05b5219..3b55225c3 100644
--- a/src/bin/mathml2text.rs
+++ b/src/bin/mathml2text.rs
@@ -18,6 +18,10 @@ fn get_rules_dir() -> String {
     return rules_path.as_os_str().to_str().unwrap().to_string();
 }
 
+fn resolve_rules_dir(rules_dir: Option<PathBuf>) -> PathBuf {
+    return rules_dir.unwrap_or_else(|| PathBuf::from(get_rules_dir()));
+}
+
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, ValueEnum)]
 enum OutputType {
     Text,
@@ -60,14 +64,15 @@ fn main() -> Result<()> {
 		"#.to_string()
     };
 
-    if let Err(e) = set_rules_dir(get_rules_dir()) {
+    let rules_dir = resolve_rules_dir(cli.rules_dir);
+    if let Err(e) = set_rules_dir(rules_dir.to_string_lossy()) {
 	panic!("Error: exiting -- {}", errors_to_string(&e));
     }
     debug!("Languages: {}", libmathcat::interface::get_supported_languages()?.join(", "));
 
     #[cfg(feature = "include-zip")]
     info!("***********include-zip is present**********");
-    info!("Version = '{}' using Rules dir {}", get_version(), get_rules_dir());
+    info!("Version = '{}' using Rules dir {}", get_version(), rules_dir.display());
     set_preference("Language", cli.language)?;
 
     set_preference("DecimalSeparator", "Auto").unwrap();
diff --git a/tests/mathml2text.rs b/tests/mathml2text.rs
new file mode 100644
index 000000000..2f9f418d3
--- /dev/null
+++ b/tests/mathml2text.rs
@@ -0,0 +1,70 @@
+mod common;
+
+use std::ffi::OsStr;
+use std::path::PathBuf;
+use std::process::{Command, Output};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+struct Mathml2TextFixture {
+    input_file: PathBuf,
+}
+
+impl Mathml2TextFixture {
+    fn new(name: &str, mathml: &str) -> Self {
+        let timestamp = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .expect("system time should be after UNIX_EPOCH")
+            .as_nanos();
+        let input_file = std::env::temp_dir().join(format!("mathml2text-{name}-{timestamp}.mml"));
+        std::fs::write(&input_file, mathml).expect("should write temp input file");
+        Self { input_file }
+    }
+
+    fn run_with_rules_dir(&self, rules_dir: impl AsRef<OsStr>) -> Output {
+        Command::new(env!("CARGO_BIN_EXE_mathml2text"))
+            .arg("--rules-dir")
+            .arg(rules_dir)
+            .arg(&self.input_file)
+            .output()
+            .expect("mathml2text should run")
+    }
+
+    fn missing_rules_dir(&self) -> PathBuf {
+        self.input_file.with_extension("missing-rules")
+    }
+}
+
+impl Drop for Mathml2TextFixture {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_file(&self.input_file);
+    }
+}
+
+/// Verifies that `mathml2text` uses an explicitly provided `--rules-dir`.
+/// This protects the CLI override path instead of silently falling back to the default rules location.
+#[test]
+fn accepts_explicit_rules_dir() {
+    let fixture = Mathml2TextFixture::new("explicit-rules", "<math><mn>4</mn></math>");
+    let output = fixture.run_with_rules_dir(common::abs_rules_dir_path());
+
+    assert!(
+        output.status.success(),
+        "stderr: {}",
+        String::from_utf8_lossy(&output.stderr)
+    );
+    assert_eq!("4\n", String::from_utf8_lossy(&output.stdout));
+}
+
+/// Verifies that an invalid explicit `--rules-dir` causes the CLI to fail.
+/// This protects against regressions where the flag is parsed but then ignored at runtime.
+#[test]
+fn rejects_invalid_explicit_rules_dir() {
+    let fixture = Mathml2TextFixture::new("invalid-rules", "<math><mn>5</mn></math>");
+    let output = fixture.run_with_rules_dir(fixture.missing_rules_dir());
+
+    assert!(
+        !output.status.success(),
+        "stdout: {}",
+        String::from_utf8_lossy(&output.stdout)
+    );
+}