diff --git a/libc/spec/posix.td b/libc/spec/posix.td
--- a/libc/spec/posix.td
+++ b/libc/spec/posix.td
@@ -984,7 +984,7 @@
       >,
       FunctionSpec<
           "pthread_exit",
-          RetValSpec<VoidType>,
+          RetValSpec<NoReturn>,
           [ArgSpec<VoidPtr>]
       >,
       FunctionSpec<
diff --git a/libc/src/pthread/pthread_exit.h b/libc/src/pthread/pthread_exit.h
--- a/libc/src/pthread/pthread_exit.h
+++ b/libc/src/pthread/pthread_exit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void pthread_exit(void *retval);
+[[noreturn]] void pthread_exit(void *retval);
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/exit.h b/libc/src/stdlib/exit.h
--- a/libc/src/stdlib/exit.h
+++ b/libc/src/stdlib/exit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void exit(int status);
+[[noreturn]] void exit(int status);
 
 } // namespace __llvm_libc