diff --git a/src/google/adk/tools/skill_toolset.py b/src/google/adk/tools/skill_toolset.py
index 514cfee52f..1f9ffe1241 100644
--- a/src/google/adk/tools/skill_toolset.py
+++ b/src/google/adk/tools/skill_toolset.py
@@ -152,7 +152,7 @@ async def run_async(
     agent_name = tool_context.agent_name
     state_key = f"_adk_activated_skill_{agent_name}"
 
-    activated_skills = list(tool_context.state.get(state_key, []))
+    activated_skills = list(tool_context.state.get(state_key) or [])
     if skill_name not in activated_skills:
       activated_skills.append(skill_name)
       tool_context.state[state_key] = activated_skills
@@ -791,7 +791,7 @@ async def _resolve_additional_tools_from_state(
 
     agent_name = readonly_context.agent_name
     state_key = f"_adk_activated_skill_{agent_name}"
-    activated_skills = readonly_context.state.get(state_key, [])
+    activated_skills = readonly_context.state.get(state_key) or []
 
     if not activated_skills:
       return []