diff --git a/AK/StdLibExtras.cpp b/AK/StdLibExtras.cpp
index b807d5ebb9..ee8aa862d9 100644
--- a/AK/StdLibExtras.cpp
+++ b/AK/StdLibExtras.cpp
@@ -5,6 +5,7 @@
 
 extern "C" {
 
+#ifndef KERNEL
 void* mmx_memcpy(void* dest, const void* src, size_t len)
 {
     ASSERT(len >= 1024);
@@ -51,6 +52,7 @@ void* mmx_memcpy(void* dest, const void* src, size_t len)
         memcpy(dest_ptr, src_ptr, len);
     return dest;
 }
+#endif
 
 #ifdef KERNEL
 
diff --git a/AK/StdLibExtras.h b/AK/StdLibExtras.h
index 04c9ce72d0..6a282b98ab 100644
--- a/AK/StdLibExtras.h
+++ b/AK/StdLibExtras.h
@@ -11,14 +11,18 @@
 
 #include <AK/Types.h>
 
+#ifndef KERNEL
 extern "C" void* mmx_memcpy(void* to, const void* from, size_t);
+#endif
 
 [[gnu::always_inline]] inline void fast_dword_copy(dword* dest, const dword* src, size_t count)
 {
+#ifndef KERNEL
     if (count >= 256) {
         mmx_memcpy(dest, src, count * sizeof(count));
         return;
     }
+#endif
     asm volatile(
         "rep movsl\n"
         : "=S"(src), "=D"(dest), "=c"(count)
diff --git a/Kernel/StdLib.cpp b/Kernel/StdLib.cpp
index 41aa2c65df..af9eacaab7 100644
--- a/Kernel/StdLib.cpp
+++ b/Kernel/StdLib.cpp
@@ -8,9 +8,10 @@ extern "C" {
 
 void* memcpy(void* dest_ptr, const void* src_ptr, size_t n)
 {
-    if (n >= 1024) {
+#ifndef KERNEL
+    if (n >= 1024)
         return mmx_memcpy(dest_ptr, src_ptr, n);
-    }
+#endif
 
     size_t dest = (size_t)dest_ptr;
     size_t src = (size_t)src_ptr;