diff --git a/src/calibre/ai/__init__.py b/src/calibre/ai/__init__.py
index 2cef259b77..e87116bb1e 100644
--- a/src/calibre/ai/__init__.py
+++ b/src/calibre/ai/__init__.py
@@ -146,3 +146,7 @@ class AICapabilities(Flag):
     @property
     def supports_text_to_image(self) -> bool:
         return AICapabilities.text_to_image in self
+
+    @property
+    def purpose(self) -> str:
+        return 'AICapabilities.'+'|'.join(sorted(x.name for x in self))
diff --git a/src/calibre/ai/config.py b/src/calibre/ai/config.py
index 78564863e8..992c6a1de1 100644
--- a/src/calibre/ai/config.py
+++ b/src/calibre/ai/config.py
@@ -68,7 +68,7 @@ class ConfigureAI(QWidget):
             return False
         p.save_settings(w)
         pmap = prefs()['purpose_map']
-        pmap[str(self.purpose)] = p.name
+        pmap[self.purpose.purpose] = p.name
         prefs().set('purpose_map', pmap)
         return True
 
diff --git a/src/calibre/ai/prefs.py b/src/calibre/ai/prefs.py
index 23893c37d4..8330e3c9a6 100644
--- a/src/calibre/ai/prefs.py
+++ b/src/calibre/ai/prefs.py
@@ -42,7 +42,7 @@ def plugins_for_purpose(purpose: AICapabilities) -> Iterator[AIProviderPlugin]:
 
 def plugin_for_purpose(purpose: AICapabilities) -> AIProviderPlugin | None:
     compatible_plugins = {p.name: p for p in plugins_for_purpose(purpose)}
-    q = prefs()['purpose_map'].get(str(purpose), '')
+    q = prefs()['purpose_map'].get(purpose.purpose, '')
     if ans := compatible_plugins.get(q):
         return ans
     if compatible_plugins: