diff --git a/src/serena/agent.py b/src/serena/agent.py
index d5b69269..953e4241 100644
--- a/src/serena/agent.py
+++ b/src/serena/agent.py
@@ -640,12 +640,10 @@ class SerenaAgent:
         # determine the effective language backend for this session.
         # If a startup project is provided and has a per-project override, use it; otherwise use the global config.
         # Since we don't want to change the toolset after startup, the language backend cannot be changed within a running Serena session
-        self._language_backend = self.serena_config.language_backend
-        if registered_project_to_activate is not None and registered_project_to_activate.project_config.language_backend is not None:
-            self._language_backend = registered_project_to_activate.project_config.language_backend
-            log.info(f"Using language backend as configured in project.yml: {self._language_backend.name}")
-        else:
-            log.info(f"Using language backend from global configuration: {self._language_backend.name}")
+        self._language_backend = self.serena_config.determine_language_backend(
+            project_config=registered_project_to_activate.project_config if registered_project_to_activate is not None else None,
+            log_choice=True,
+        )
 
         # create the tool names mapping for prompts
         self._prompt_tool_names_mapping = self._create_prompt_tool_names_mapping(self._language_backend)
diff --git a/src/serena/config/serena_config.py b/src/serena/config/serena_config.py
index 0b8fc673..2b580082 100644
--- a/src/serena/config/serena_config.py
+++ b/src/serena/config/serena_config.py
@@ -1297,3 +1297,14 @@ class SerenaConfig(SharedConfig, ModeSelectionDefinitionWithBaseModes):
             if glob_match(pattern, project_root_str):
                 return True
         return False
+
+    def determine_language_backend(self, project_config: ProjectConfig | None = None, log_choice: bool = False):
+        language_backend = self.language_backend
+        if project_config and project_config.language_backend is not None:
+            language_backend = project_config.language_backend
+            if log_choice:
+                log.info(f"Using language backend as configured in project: {language_backend.name}")
+        else:
+            if log_choice:
+                log.info(f"Using language backend from global configuration: {language_backend.name}")
+        return language_backend
diff --git a/src/serena/project.py b/src/serena/project.py
index e40c2dab..87d0f969 100644
--- a/src/serena/project.py
+++ b/src/serena/project.py
@@ -9,6 +9,7 @@ from sensai.util.logging import LogTime
 from sensai.util.string import TextBuilder, ToStringMixin
 
 from serena.config.serena_config import (
+    LanguageBackend,
     ProjectConfig,
     SerenaConfig,
 )
@@ -121,6 +122,16 @@ class Project(ToStringMixin):
     def project_name(self) -> str:
         return self.project_config.project_name
 
+    @property
+    def language_backend(self) -> LanguageBackend:
+        # The backend configuration is fundamentally owned by the agent, so it takes
+        # precedence. (Note: The agent does not necessary honour the project's choice,
+        # as it may be invalid.)
+        if self._agent is not None:
+            return self._agent.get_language_backend()
+        else:
+            return self.serena_config.determine_language_backend(self.project_config)
+
     @classmethod
     def load(
         cls,