diff --git a/Userland/Libraries/LibC/sys/mman.cpp b/Userland/Libraries/LibC/sys/mman.cpp
index 101860fafc..3f361e50a8 100644
--- a/Userland/Libraries/LibC/sys/mman.cpp
+++ b/Userland/Libraries/LibC/sys/mman.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Format.h>
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
@@ -82,4 +83,10 @@ void* allocate_tls(const char* initial_data, size_t size)
     }
     return (void*)rc;
 }
+
+int mlock(const void*, size_t)
+{
+    dbgln("FIXME: Implement mlock()");
+    return 0;
+}
 }
diff --git a/Userland/Libraries/LibC/sys/mman.h b/Userland/Libraries/LibC/sys/mman.h
index 0207e47b72..960c84d533 100644
--- a/Userland/Libraries/LibC/sys/mman.h
+++ b/Userland/Libraries/LibC/sys/mman.h
@@ -41,5 +41,6 @@ int mprotect(void*, size_t, int prot);
 int set_mmap_name(void*, size_t, const char*);
 int madvise(void*, size_t, int advice);
 void* allocate_tls(const char* initial_data, size_t);
+int mlock(const void*, size_t);
 
 __END_DECLS