diff --git a/conductor/tracks/ts_cpp_tree_sitter_20260308/plan.md b/conductor/tracks/ts_cpp_tree_sitter_20260308/plan.md
index 9fd81bf..0fddf95 100644
--- a/conductor/tracks/ts_cpp_tree_sitter_20260308/plan.md
+++ b/conductor/tracks/ts_cpp_tree_sitter_20260308/plan.md
@@ -48,7 +48,7 @@ Focus: Implement definitions, signatures, and update tools
 - [x] Task 5.1: Implement get_definition for C and C++ 799feb0
 - [x] Task 5.2: Implement get_signature for C and C++ 799feb0
 
-- [ ] Task 5.3: Implement update_definition for C and C++
+- [x] Task 5.3: Implement update_definition for C and C++ 8642d89
   - WHERE: src/mcp_client.py
   - WHAT: Implement `ts_c_update_definition` and `ts_cpp_update_definition`
   - HOW: Use AST to find target range; surgically replace lines in file