diff --git a/libc/include/semaphore.h b/libc/include/semaphore.h
index 5d66f7e..6ad9ea3 100644
--- a/libc/include/semaphore.h
+++ b/libc/include/semaphore.h
@@ -45,12 +45,12 @@
 
 #define SEM_FAILED __BIONIC_CAST(reinterpret_cast, sem_t*, 0)
 
-int sem_clockwait(sem_t* __sem, clockid_t __clock, const struct timespec* __ts) __INTRODUCED_IN(30);
-int sem_destroy(sem_t* __sem);
-int sem_getvalue(sem_t* __sem, int* __value);
-int sem_init(sem_t* __sem, int __shared, unsigned int __value);
-int sem_post(sem_t* __sem);
-int sem_timedwait(sem_t* __sem, const struct timespec* __ts);
+int sem_clockwait(sem_t* _Nonnull __sem, clockid_t __clock, const struct timespec* _Nonnull __ts) __INTRODUCED_IN(30);
+int sem_destroy(sem_t* _Nonnull __sem);
+int sem_getvalue(sem_t* _Nonnull __sem, int* _Nonnull __value);
+int sem_init(sem_t* _Nonnull __sem, int __shared, unsigned int __value);
+int sem_post(sem_t* _Nonnull __sem);
+int sem_timedwait(sem_t* _Nonnull __sem, const struct timespec* _Nonnull __ts);
 /*
  * POSIX historically only supported using sem_timedwait() with CLOCK_REALTIME, however that is
  * typically inappropriate, since that clock can change dramatically, causing the timeout to either
@@ -59,14 +59,14 @@
  * Note that sem_clockwait() allows specifying an arbitrary clock and has superseded this
  * function.
  */
-int sem_timedwait_monotonic_np(sem_t* __sem, const struct timespec* __ts) __INTRODUCED_IN(28);
-int sem_trywait(sem_t* __sem);
-int sem_wait(sem_t* __sem);
+int sem_timedwait_monotonic_np(sem_t* _Nonnull __sem, const struct timespec* _Nonnull __ts) __INTRODUCED_IN(28);
+int sem_trywait(sem_t* _Nonnull __sem);
+int sem_wait(sem_t* _Nonnull __sem);
 
 /* These aren't actually implemented. */
-sem_t* sem_open(const char* __name, int _flags, ...);
-int sem_close(sem_t* __sem);
-int sem_unlink(const char* __name);
+sem_t* _Nullable sem_open(const char* _Nonnull __name, int _flags, ...);
+int sem_close(sem_t* _Nonnull __sem);
+int sem_unlink(const char* _Nonnull __name);
 
 __END_DECLS
 
diff --git a/libc/include/setjmp.h b/libc/include/setjmp.h
index 141e925..6d047ae 100644
--- a/libc/include/setjmp.h
+++ b/libc/include/setjmp.h
@@ -47,14 +47,33 @@
 #include <sys/cdefs.h>
 
 #if defined(__aarch64__)
+/**
+ * The size in words of an arm64 jmp_buf. Room for callee-saved registers,
+ * including floating point, stack pointer and program counter, various
+ * internal implementation details, and leaving some free space.
+ *
+ * Coincidentally matches OpenBSD, though they also save/restore the
+ * floating point status register too.
+ */
 #define _JBLEN 32
 #elif defined(__arm__)
+/** The size in words of an arm32 jmp_buf. Inherited from OpenBSD. */
 #define _JBLEN 64
 #elif defined(__i386__)
+/** The size in words of an x86 jmp_buf. Inherited from OpenBSD. */
 #define _JBLEN 10
 #elif defined(__riscv)
+/**
+ * The size in words of a riscv64 jmp_buf. Room for callee-saved registers,
+ * including floating point, stack pointer and program counter, various
+ * internal implementation details, and leaving some free space.
+ *
+ * Coincidentally matches OpenBSD, though they also save/restore the
+ * floating point status register too.
+ */
 #define _JBLEN 32
 #elif defined(__x86_64__)
+/** The size in words of an x86-64 jmp_buf. Inherited from OpenBSD. */
 #define _JBLEN 11
 #endif
 
diff --git a/tests/semaphore_test.cpp b/tests/semaphore_test.cpp
index f3f6020..6f8797f 100644
--- a/tests/semaphore_test.cpp
+++ b/tests/semaphore_test.cpp
@@ -165,8 +165,10 @@
 TEST_F(semaphore_DeathTest, sem_timedwait_null_timeout) {
   sem_t s;
   ASSERT_EQ(0, sem_init(&s, 0, 0));
-
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnonnull"
   ASSERT_EXIT(sem_timedwait(&s, nullptr), testing::KilledBySignal(SIGSEGV), "");
+#pragma clang diagnostic pop
 }
 
 TEST(semaphore, sem_getvalue) {