diff --git a/Userland/Libraries/LibPthread/pthread.cpp b/Userland/Libraries/LibPthread/pthread.cpp
index 1dc878f210..493657de69 100644
--- a/Userland/Libraries/LibPthread/pthread.cpp
+++ b/Userland/Libraries/LibPthread/pthread.cpp
@@ -740,4 +740,9 @@ int pthread_rwlockattr_setpshared(pthread_rwlockattr_t*, int)
     ASSERT_NOT_REACHED();
 }
 
+int pthread_atfork(void (*)(void), void (*)(void), void (*)(void))
+{
+    ASSERT_NOT_REACHED();
+}
+
 } // extern "C"
diff --git a/Userland/Libraries/LibPthread/pthread.h b/Userland/Libraries/LibPthread/pthread.h
index 5994ae1009..e9fe3389d8 100644
--- a/Userland/Libraries/LibPthread/pthread.h
+++ b/Userland/Libraries/LibPthread/pthread.h
@@ -145,4 +145,6 @@ int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t* __restrict, int* _
 int pthread_rwlockattr_init(pthread_rwlockattr_t*);
 int pthread_rwlockattr_setpshared(pthread_rwlockattr_t*, int);
 
+int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void));
+
 __END_DECLS