diff --git a/libc/bionic/pthread_getcpuclockid.cpp b/libc/bionic/pthread_getcpuclockid.cpp
index 10046ba..d11f56a 100644
--- a/libc/bionic/pthread_getcpuclockid.cpp
+++ b/libc/bionic/pthread_getcpuclockid.cpp
@@ -36,7 +36,13 @@
     return ESRCH;
   }
 
-  enum { CLOCK_IDTYPE_BITS = 3 };
-  *clockid = CLOCK_THREAD_CPUTIME_ID | (thread->tid << CLOCK_IDTYPE_BITS);
+  // The tid is stored in the top bits, but negated.
+  clockid_t result = ~static_cast<clockid_t>(thread->tid) << 3;
+  // Bits 0 and 1: clock type (0 = CPUCLOCK_PROF, 1 = CPUCLOCK_VIRT, 2 = CPUCLOCK_SCHED).
+  result |= 2;
+  // Bit 2: thread (set) or process (clear)?
+  result |= (1 << 2);
+
+  *clockid = result;
   return 0;
 }