diff --git a/dlls/kernel32/kernel32.spec b/dlls/kernel32/kernel32.spec
index 8e97cdb6f7..f9a0770b7c 100644
--- a/dlls/kernel32/kernel32.spec
+++ b/dlls/kernel32/kernel32.spec
@@ -1284,7 +1284,7 @@
 @ stdcall -register RtlCaptureContext(ptr) ntdll.RtlCaptureContext
 @ stdcall RtlCaptureStackBackTrace(long long ptr ptr) ntdll.RtlCaptureStackBackTrace
 @ stdcall -arch=x86_64 RtlCompareMemory(ptr ptr long) ntdll.RtlCompareMemory
-# @ stub -arch=x86_64 RtlCopyMemory
+@ stdcall -arch=x86_64 RtlCopyMemory(ptr ptr long) ntdll.RtlCopyMemory
 @ cdecl -arch=arm,x86_64 RtlDeleteFunctionTable(ptr) ntdll.RtlDeleteFunctionTable
 @ stdcall RtlFillMemory(ptr long long) ntdll.RtlFillMemory
 @ cdecl -arch=x86_64 RtlInstallFunctionTableCallback(long long long ptr ptr ptr) ntdll.RtlInstallFunctionTableCallback
diff --git a/dlls/ntdll/ntdll.spec b/dlls/ntdll/ntdll.spec
index 191115bbd4..270d7ff8d1 100644
--- a/dlls/ntdll/ntdll.spec
+++ b/dlls/ntdll/ntdll.spec
@@ -474,6 +474,7 @@
 # @ stub RtlConvertVariantToProperty
 @ stdcall RtlCopyLuid(ptr ptr)
 @ stdcall RtlCopyLuidAndAttributesArray(long ptr ptr)
+@ stdcall -arch=x86_64 RtlCopyMemory(ptr ptr long)
 # @ stub RtlCopyMemoryStreamTo
 # @ stub RtlCopyOutOfProcessMemoryStreamTo
 # @ stub RtlCopyRangeList
diff --git a/dlls/ntdll/rtl.c b/dlls/ntdll/rtl.c
index 8f6f386e45..855bdb96c5 100644
--- a/dlls/ntdll/rtl.c
+++ b/dlls/ntdll/rtl.c
@@ -533,6 +533,15 @@ SIZE_T WINAPI RtlCompareMemoryUlong(const ULONG *Source1, SIZE_T Length, ULONG d
     return i * sizeof(ULONG);
 }
 
+/******************************************************************************
+ *  RtlCopyMemory   [NTDLL.@]
+ */
+#undef RtlCopyMemory
+void WINAPI RtlCopyMemory(void *dest, const void *src, SIZE_T len)
+{
+    memcpy(dest, src, len);
+}
+
 /******************************************************************************
  *  RtlAssert                           [NTDLL.@]
  *