diff -urNad mapserver-6.0.0~/mapunion.c mapserver-6.0.0/mapunion.c
--- mapserver-6.0.0/mapunion.c	(revision 11709)
+++ mapserver-6.0.0/mapunion.c	(revision 11714)
@@ -316,5 +316,5 @@
             /* get items requested by the union layer plus the required items */
             msLayerSetProcessingKey(srclayer, "ITEMS", itemlist);
-            if (msLayerWhichItems(srclayer, TRUE, NULL) != MS_SUCCESS)
+            if (msLayerWhichItems(srclayer, MS_TRUE, NULL) != MS_SUCCESS)
             {
                 msFree(itemlist);
@@ -325,5 +325,5 @@
         {
             /* get only the required items */
-            if (msLayerWhichItems(srclayer, FALSE, NULL) != MS_SUCCESS)
+            if (msLayerWhichItems(srclayer, MS_FALSE, NULL) != MS_SUCCESS)
                 return MS_FAILURE;
         }
@@ -354,5 +354,5 @@
             
             /* get only the required items */
-            if (msLayerWhichItems(srclayer, FALSE, NULL) != MS_SUCCESS)
+            if (msLayerWhichItems(srclayer, MS_FALSE, NULL) != MS_SUCCESS)
                 return MS_FAILURE;
         }