diff --git a/kagi-test.el b/kagi-test.el
index 3c61457..41959c3 100644
--- a/kagi-test.el
+++ b/kagi-test.el
@@ -254,7 +254,7 @@ https://www.example.com"
     (describe "kagi-summarize"
       :var ((kagi-summarizer-default-language))
       (before-each
-        (setq kagi-summarizer-default-language "XY"))
+        (setq kagi-summarizer-default-language "NL"))
       (it "returns a summary on minimal text input"
         (expect (kagi-summarize just-enough-text-input) :to-equal dummy-output))
       (it "makes exactly one API call"
@@ -287,11 +287,16 @@ https://www.example.com"
       (it "falls back to the default language for invalid language codes"
         (expect (kagi-summarize just-enough-text-input "VL") :to-equal dummy-output)
         (let ((args (car (spy-calls-args-for #'kagi--call-summarizer 0))))
-          (expect (map-elt args "target_language") :to-equal "XY")))
+          (expect (map-elt args "target_language") :to-equal "NL")))
       (it "falls back to the default language for invalid language names"
         (expect (kagi-summarize just-enough-text-input "Valyrian") :to-equal dummy-output)
         (let ((args (car (spy-calls-args-for #'kagi--call-summarizer 0))))
-          (expect (map-elt args "target_language") :to-equal "XY")))
+          (expect (map-elt args "target_language") :to-equal "NL")))
+      (it "falls back to English if the default language is invalid"
+        (setq kagi-summarizer-default-language "XY")
+        (expect (kagi-summarize just-enough-text-input "Valyrian") :to-equal dummy-output)
+        (let ((args (car (spy-calls-args-for #'kagi--call-summarizer 0))))
+          (expect (map-elt args "target_language") :to-equal "EN")))
       (it "returns a summary for an HTTPS URL"
         (expect (kagi-summarize dummy-https-url) :to-equal dummy-output))
       (it "returns a summary for an uppercase HTTPS URL"
diff --git a/kagi.el b/kagi.el
index 026b88b..e150fd8 100644
--- a/kagi.el
+++ b/kagi.el
@@ -513,25 +513,31 @@ no issues."
   "Non-nil if string S is a URL."
   (string-match-p (rx (seq bos "http" (? "s") "://" (+ (not space)) eos)) s))
 
+(defun kagi--valid-language-name-p (language)
+  "Return non-nil if LANGUAGE is a valid language name."
+  (and (stringp language)
+       (map-elt kagi--summarizer-languages (capitalize language))))
+
+(defun kagi--valid-language-code-p (language)
+  "Return t if LANGUAGE is a valid two letter language code for the summarizer."
+  (and (stringp language)
+       (seq-contains-p
+        (map-values kagi--summarizer-languages)
+        (upcase language))))
+
 (defun kagi--summarizer-determine-language (hint)
   "Determine the language for the summary given a language HINT.
 
 The HINT may be a language code (e.g. `DE') or a language
-name (e.g. `GERMAN'). If as invalid hint is given, it falls back
+name (e.g. `German'). If as invalid hint is given, it falls back
 to `kagi-summarizer-default-language'."
-  (if (stringp hint)
-      (or
-       ;; check language code
-       (map-elt kagi--summarizer-languages (capitalize hint))
-       ;; not a valid code, check it as a name
-       (and (seq-contains-p
-             (map-values kagi--summarizer-languages)
-             (upcase hint))
-            (upcase hint))
-       ;; neither valid code or name, fallback
-       kagi-summarizer-default-language)
-    ;; hint was nil or something else, fallback
-    kagi-summarizer-default-language))
+  (cond
+   ((kagi--valid-language-code-p hint) (upcase hint))
+   ((kagi--valid-language-name-p hint)
+    (map-elt kagi--summarizer-languages (capitalize hint)))
+   ((kagi--valid-language-code-p kagi-summarizer-default-language)
+    kagi-summarizer-default-language)
+   (t "EN")))
 
 (defun kagi-summarize (text-or-url &optional language engine format)
   "Return the summary of the given TEXT-OR-URL.