diff --git a/src/backend.rs b/src/backend.rs
index d35f857..af54a9f 100644
--- a/src/backend.rs
+++ b/src/backend.rs
@@ -141,6 +141,28 @@ impl Default for VulkanBackend {
     }
 }
 
+/// Validate that a provided language hint is compatible with the selected model.
+///
+/// English-only models (filenames containing ".en." or ending with ".en.bin") reject non-"en" hints.
+/// When no language is provided, this check passes and downstream behavior remains unchanged.
+pub(crate) fn validate_model_lang_compat(model: &Path, lang_opt: Option<&str>) -> Result<()> {
+    let is_en_only = model
+        .file_name()
+        .and_then(|s| s.to_str())
+        .map(|s| s.contains(".en.") || s.ends_with(".en.bin"))
+        .unwrap_or(false);
+    if let Some(lang) = lang_opt {
+        if is_en_only && lang != "en" {
+            return Err(anyhow!(
+                "Selected model is English-only ({}), but a non-English language hint '{}' was provided. Please use a multilingual model or set WHISPER_MODEL.",
+                model.display(),
+                lang
+            ));
+        }
+    }
+    Ok(())
+}
+
 impl TranscribeBackend for CpuBackend {
     fn kind(&self) -> BackendKind {
         BackendKind::Cpu
@@ -328,20 +350,8 @@ pub(crate) fn transcribe_with_whisper_rs(
             note: Some("model selected".to_string()),
         });
     }
-    let is_en_only = model
-        .file_name()
-        .and_then(|s| s.to_str())
-        .map(|s| s.contains(".en.") || s.ends_with(".en.bin"))
-        .unwrap_or(false);
-    if let Some(lang) = lang_opt {
-        if is_en_only && lang != "en" {
-            return Err(anyhow!(
-                "Selected model is English-only ({}), but a non-English language hint '{}' was provided. Please use a multilingual model or set WHISPER_MODEL.",
-                model.display(),
-                lang
-            ));
-        }
-    }
+    // Validate language hint compatibility with the selected model
+    validate_model_lang_compat(&model, lang_opt)?;
     let model_str = model
         .to_str()
         .ok_or_else(|| anyhow!("Model path not valid UTF-8: {}", model.display()))?;
@@ -451,6 +461,35 @@ mod tests {
     use std::env as std_env;
     use std::sync::{Mutex, OnceLock};
 
+    #[test]
+    fn test_validate_model_lang_guard_table() {
+        struct case<'a> { model: &'a str, lang: Option<&'a str>, ok: bool }
+        let cases = vec![
+            // English-only model with en hint: OK
+            case { model: "ggml-base.en.bin", lang: Some("en"), ok: true },
+            // English-only model with de hint: Error
+            case { model: "ggml-small.en.bin", lang: Some("de"), ok: false },
+            // Multilingual model with de hint: OK
+            case { model: "ggml-large-v3.bin", lang: Some("de"), ok: true },
+            // No language provided (audio path scenario): guard should pass (existing behavior elsewhere)
+            case { model: "ggml-medium.en.bin", lang: None, ok: true },
+        ];
+        for c in cases {
+            let p = std::path::Path::new(c.model);
+            let res = validate_model_lang_compat(p, c.lang);
+            match (c.ok, res) {
+                (true, Ok(())) => {}
+                (false, Err(e)) => {
+                    let msg = format!("{}", e);
+                    assert!(msg.contains("English-only"), "unexpected error: {msg}");
+                    if let Some(l) = c.lang { assert!(msg.contains(l), "missing lang in msg: {msg}"); }
+                }
+                (true, Err(e)) => panic!("expected Ok for model={}, lang={:?}, got error: {}", c.model, c.lang, e),
+                (false, Ok(())) => panic!("expected Err for model={}, lang={:?}", c.model, c.lang),
+            }
+        }
+    }
+
     // Serialize environment variable modifications across tests in this module
     static ENV_LOCK: OnceLock<Mutex<()>> = OnceLock::new();