diff --git a/progress.md b/progress.md
index b9c828a..cbb83f1 100644
--- a/progress.md
+++ b/progress.md
@@ -80,7 +80,7 @@
 - [x] Chapter 9: Concurrency with Shared Variables
  - [ ] 9.1 Race Conditions
  - [ ] 9.2 Mutual Exclusion: sync.Mutex
- - [ ] 9.3 Read/Write Mutexes: sync.RWMutex
+ - [x] 9.3 Read/Write Mutexes: sync.RWMutex
  - [ ] 9.4 Memory Synchronization
  - [ ] 9.5 Lazy Initialization: sync.Once
  - [ ] 9.6 The Race Detector