diff --git a/Userland/Libraries/LibC/sys/mman.cpp b/Userland/Libraries/LibC/sys/mman.cpp
index faee202e00..df796f3e86 100644
--- a/Userland/Libraries/LibC/sys/mman.cpp
+++ b/Userland/Libraries/LibC/sys/mman.cpp
@@ -94,6 +94,13 @@ int mlock(const void*, size_t)
     return 0;
 }
 
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/munlock.html
+int munlock(const void*, size_t)
+{
+    dbgln("FIXME: Implement munlock()");
+    return 0;
+}
+
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/msync.html
 int msync(void* address, size_t size, int flags)
 {
diff --git a/Userland/Libraries/LibC/sys/mman.h b/Userland/Libraries/LibC/sys/mman.h
index c1eacbe127..1a304478fd 100644
--- a/Userland/Libraries/LibC/sys/mman.h
+++ b/Userland/Libraries/LibC/sys/mman.h
@@ -20,6 +20,7 @@ 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);
+int munlock(const void*, size_t);
 int msync(void*, size_t, int flags);
 
 __END_DECLS