diff --git a/js/xpconnect/src/xpc.msg b/js/xpconnect/src/xpc.msg
index 2c99c27eb00..b63fd1b7517 100644
--- a/js/xpconnect/src/xpc.msg
+++ b/js/xpconnect/src/xpc.msg
@@ -121,8 +121,6 @@ XPC_MSG_DEF(NS_ERROR_FACTORY_REGISTER_AGAIN        , "Factory not registered (ma
 XPC_MSG_DEF(NS_ERROR_FACTORY_NOT_LOADED            , "Factory not loaded")
 XPC_MSG_DEF(NS_ERROR_FACTORY_NO_SIGNATURE_SUPPORT  , "Factory does not support signatures")
 XPC_MSG_DEF(NS_ERROR_FACTORY_EXISTS                , "Factory already exists")
-XPC_MSG_DEF(NS_ERROR_PROXY_INVALID_IN_PARAMETER    , "Invalid input parameter in call to proxy")
-XPC_MSG_DEF(NS_ERROR_PROXY_INVALID_OUT_PARAMETER   , "Invalid output parameter in call to proxy")
 
 /* added from nsError.h on Feb 28 2001... */
 
diff --git a/xpcom/base/nsError.h b/xpcom/base/nsError.h
index c6d866bdecc..d014c5bea2d 100644
--- a/xpcom/base/nsError.h
+++ b/xpcom/base/nsError.h
@@ -228,33 +228,6 @@ inline int NS_SUCCEEDED(nsresult _nsresult) {
 #define NS_ERROR_FACTORY_EXISTS            (NS_ERROR_BASE + 0x100)
 
 
-/* For COM compatibility reasons, we want to use exact error code numbers
-   for NS_ERROR_PROXY_INVALID_IN_PARAMETER and NS_ERROR_PROXY_INVALID_OUT_PARAMETER.
-   The first matches:
-
-     #define RPC_E_INVALID_PARAMETER          _HRESULT_TYPEDEF_(0x80010010L)
-
-   Errors returning this mean that the xpcom proxy code could not create a proxy for
-   one of the in paramaters.
-
-   Because of this, we are ignoring the convention if using a base and offset for
-   error numbers.
-
-*/
-
-/* Returned when a proxy could not be create a proxy for one of the IN parameters
-   This is returned only when the "real" method has NOT been invoked.
-*/
-
-#define NS_ERROR_PROXY_INVALID_IN_PARAMETER        ((nsresult) 0x80010010L)
-
-/* Returned when a proxy could not be create a proxy for one of the OUT parameters
-   This is returned only when the "real" method has ALREADY been invoked.
-*/
-
-#define NS_ERROR_PROXY_INVALID_OUT_PARAMETER       ((nsresult) 0x80010011L)
-
-
 /*@}*/
 
  /* I/O Errors */