diff --git a/libc/include/sys/_system_properties.h b/libc/include/sys/_system_properties.h
index c7a30eb..1afb000 100644
--- a/libc/include/sys/_system_properties.h
+++ b/libc/include/sys/_system_properties.h
@@ -62,7 +62,7 @@
 ** This was previously for testing, but now that SystemProperties is its own testable class,
 ** there is never a reason to call this function and its implementation simply returns -1.
 */
-int __system_property_set_filename(const char* __filename);
+int __system_property_set_filename(const char* __unused __filename);
 
 /*
 ** Initialize the area to be used to store properties.  Can
@@ -103,7 +103,7 @@
 **
 ** Returns 0 on success, -1 if the property area is full.
 */
-int __system_property_add(const char* __name, unsigned int __name_length, const char* __value, unsigned int __value_length);
+int __system_property_add(const char* _Nonnull __name, unsigned int __name_length, const char* _Nonnull __value, unsigned int __value_length);
 
 /* Update the value of a system property returned by
 ** __system_property_find.  Can only be done by a single process
@@ -113,14 +113,14 @@
 **
 ** Returns 0 on success, -1 if the parameters are incorrect.
 */
-int __system_property_update(prop_info* __pi, const char* __value, unsigned int __value_length);
+int __system_property_update(prop_info* _Nonnull __pi, const char* _Nonnull __value, unsigned int __value_length);
 
 /* Read the serial number of a system property returned by
 ** __system_property_find.
 **
 ** Returns the serial number on success, -1 on error.
 */
-uint32_t __system_property_serial(const prop_info* __pi);
+uint32_t __system_property_serial(const prop_info* _Nonnull __pi);
 
 /* Initialize the system properties area in read only mode.
  * Should be done by all processes that need to read system
diff --git a/libc/include/sys/system_properties.h b/libc/include/sys/system_properties.h
index a2e1923..06b2188 100644
--- a/libc/include/sys/system_properties.h
+++ b/libc/include/sys/system_properties.h
@@ -43,7 +43,7 @@
 /*
  * Sets system property `name` to `value`, creating the system property if it doesn't already exist.
  */
-int __system_property_set(const char* __name, const char* __value);
+int __system_property_set(const char* _Nonnull __name, const char* _Nonnull __value);
 
 /*
  * Returns a `prop_info` corresponding system property `name`, or nullptr if it doesn't exist.
@@ -51,14 +51,14 @@
  *
  * Property lookup is expensive, so it can be useful to cache the result of this function.
  */
-const prop_info* __system_property_find(const char* __name);
+const prop_info* _Nullable __system_property_find(const char* _Nonnull __name);
 
 /*
  * Calls `callback` with a consistent trio of name, value, and serial number for property `pi`.
  */
-void __system_property_read_callback(const prop_info* __pi,
-    void (*__callback)(void* __cookie, const char* __name, const char* __value, uint32_t __serial),
-    void* __cookie) __INTRODUCED_IN(26);
+void __system_property_read_callback(const prop_info* _Nonnull __pi,
+    void (* _Nonnull __callback)(void* _Nullable __cookie, const char* _Nonnull __name, const char* _Nonnull __value, uint32_t __serial),
+    void* _Nullable __cookie) __INTRODUCED_IN(26);
 
 /*
  * Passes a `prop_info` for each system property to the provided
@@ -66,13 +66,13 @@
  *
  * This method is for inspecting and debugging the property system, and not generally useful.
  */
-int __system_property_foreach(void (*__callback)(const prop_info* __pi, void* __cookie), void* __cookie)
+int __system_property_foreach(void (* _Nonnull __callback)(const prop_info* _Nonnull __pi, void* _Nullable __cookie), void* _Nullable __cookie)
   __INTRODUCED_IN(19);
 
 /*
  * Waits for the specific system property identified by `pi` to be updated
  * past `old_serial`. Waits no longer than `relative_timeout`, or forever
- * if `relaive_timeout` is null.
+ * if `relative_timeout` is null.
  *
  * If `pi` is null, waits for the global serial number instead.
  *
@@ -82,17 +82,17 @@
  * timed out.
  */
 struct timespec;
-bool __system_property_wait(const prop_info* __pi, uint32_t __old_serial, uint32_t* __new_serial_ptr, const struct timespec* __relative_timeout)
+bool __system_property_wait(const prop_info* _Nullable __pi, uint32_t __old_serial, uint32_t* _Nonnull __new_serial_ptr, const struct timespec* _Nullable __relative_timeout)
     __INTRODUCED_IN(26);
 
 /* Deprecated. In Android O and above, there's no limit on property name length. */
 #define PROP_NAME_MAX   32
 /* Deprecated. Use __system_property_read_callback instead. */
-int __system_property_read(const prop_info* __pi, char* __name, char* __value);
+int __system_property_read(const prop_info* _Nonnull __pi, char* _Nullable __name, char* _Nonnull __value);
 /* Deprecated. Use __system_property_read_callback instead. */
-int __system_property_get(const char* __name, char* __value);
+int __system_property_get(const char* _Nonnull __name, char* _Nonnull __value);
 /* Deprecated. Use __system_property_foreach instead. */
-const prop_info* __system_property_find_nth(unsigned __n);
+const prop_info* _Nullable __system_property_find_nth(unsigned __n);
 
 __END_DECLS