diff --git a/dlls/advapi32/security.c b/dlls/advapi32/security.c
index fcec270fd2f..ac610055f58 100644
--- a/dlls/advapi32/security.c
+++ b/dlls/advapi32/security.c
@@ -1711,10 +1711,13 @@ BOOL WINAPI AddAce(
     return set_ntstatus(RtlAddAce(pAcl, dwAceRevision, dwStartingAceIndex, pAceList, nAceListLength));
 }
 
+/******************************************************************************
+ *  AddMandatoryAce [ADVAPI32.@]
+ */
 BOOL WINAPI AddMandatoryAce(ACL *acl, DWORD ace_revision, DWORD ace_flags, DWORD mandatory_policy, PSID label_sid)
 {
-    FIXME("%p %x %x %x %p - stub\n", acl, ace_revision, ace_flags, mandatory_policy, label_sid);
-    return FALSE;
+    return set_ntstatus(RtlAddMandatoryAce(acl, ace_revision, ace_flags, mandatory_policy,
+                                           SYSTEM_MANDATORY_LABEL_ACE_TYPE, label_sid));
 }
 
 /******************************************************************************
diff --git a/include/winbase.h b/include/winbase.h
index 4ec6f9a9db0..289f6e93f28 100644
--- a/include/winbase.h
+++ b/include/winbase.h
@@ -1693,6 +1693,7 @@ WINBASEAPI ATOM        WINAPI AddAtomW(LPCWSTR);
 #define                       AddAtom WINELIB_NAME_AW(AddAtom)
 WINADVAPI  BOOL        WINAPI AddAuditAccessAce(PACL,DWORD,DWORD,PSID,BOOL,BOOL);
 WINADVAPI  BOOL        WINAPI AddAuditAccessAceEx(PACL,DWORD,DWORD,DWORD,PSID,BOOL,BOOL);
+WINADVAPI  BOOL        WINAPI AddMandatoryAce(PACL,DWORD,DWORD,DWORD,PSID);
 WINBASEAPI VOID        WINAPI AddRefActCtx(HANDLE);
 WINBASEAPI PVOID       WINAPI AddVectoredExceptionHandler(ULONG,PVECTORED_EXCEPTION_HANDLER);
 WINADVAPI  BOOL        WINAPI AdjustTokenGroups(HANDLE,BOOL,PTOKEN_GROUPS,DWORD,PTOKEN_GROUPS,PDWORD);