diff --git a/libc/bionic/pthread_setname_np.cpp b/libc/bionic/pthread_setname_np.cpp
index 669ef04..6d2880e 100644
--- a/libc/bionic/pthread_setname_np.cpp
+++ b/libc/bionic/pthread_setname_np.cpp
@@ -43,7 +43,12 @@
 #define MAX_TASK_COMM_LEN 16
 
 static int __open_task_comm_fd(pthread_t t, int flags) {
-  pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(t);
+  pthread_internal_t* thread = __pthread_internal_find(t);
+  if (thread == nullptr) {
+    errno = ENOENT;
+    return -1;
+  }
+
   char comm_name[64];
   snprintf(comm_name, sizeof(comm_name), "/proc/self/task/%d/comm", thread->tid);
   return open(comm_name, O_CLOEXEC | flags);