diff --git a/libc/bionic/pthread_detach.cpp b/libc/bionic/pthread_detach.cpp
index 7ae5eb4..9f957f4 100644
--- a/libc/bionic/pthread_detach.cpp
+++ b/libc/bionic/pthread_detach.cpp
@@ -45,7 +45,7 @@
     switch (old_state) {
       case THREAD_NOT_JOINED: return 0;
       case THREAD_JOINED:     return 0;  // Already being joined; silently do nothing, like glibc.
-      case THREAD_DETACHED:   return THREAD_DETACHED;
+      case THREAD_DETACHED:   return EINVAL;
       case THREAD_EXITED_NOT_JOINED: break;  // Call pthread_join out of scope of pthread_accessor.
     }
   }