diff --git a/libc/include/limits.h b/libc/include/limits.h
index 80fc45d..e1f566c 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -148,9 +148,15 @@
 
 /* >= _POSIX_THREAD_DESTRUCTOR_ITERATIONS */
 #define PTHREAD_DESTRUCTOR_ITERATIONS 4
-/* >= _POSIX_THREAD_KEYS_MAX */
+
+/**
+ * The number of calls to pthread_key_create() without intervening calls to
+ * pthread_key_delete() that are guaranteed to succeed. See pthread_key_create()
+ * for more details and ways to avoid hitting this limit.
+ */
 #define PTHREAD_KEYS_MAX 128
-/* bionic has no specific limit */
+
+/** bionic has no specific limit on the number of threads. */
 #undef PTHREAD_THREADS_MAX
 
 #endif /* !_LIMITS_H_ */