Index: xrdb.c
===================================================================
RCS file: /cvs/XF4/xc/programs/xrdb/xrdb.c,v
retrieving revision 1.2
diff -u -r1.2 xrdb.c
--- xrdb.c	3 Nov 2004 00:22:58 -0000	1.2
+++ xrdb.c	27 May 2005 20:57:56 -0000
@@ -487,8 +487,11 @@
 		*val = '=';
 	    } else
 		AddSimpleDef(buff, arg + 2);
-	} else
+	} else if (arg[1] == 'U') {
 	    AddUndef(buff, arg + 2);
+	} else if (!strcmp(arg, "-undef") && oper != OPSYMBOLS) {
+	    addstring(buff, " -undef");
+	}
     }
 }
 
@@ -869,6 +872,13 @@
 		    cmd_defines[num_cmd_defines++] = arg;
 		} else {
 		    fatal("%s: Too many -U/-D arguments\n", ProgramName);
+		}
+		continue;
+	    } else if (!strcmp ("-undef", arg)) {
+		if (num_cmd_defines < MAX_CMD_DEFINES) {
+		    cmd_defines[num_cmd_defines++] = "-undef";
+		} else {
+		    fatal("%s: Too many cpp arguments\n", ProgramName);
 		}
 		continue;
 	    }
Index: xrdb.man
===================================================================
RCS file: /cvs/XF4/xc/programs/xrdb/xrdb.man,v
retrieving revision 1.2
diff -u -r1.2 xrdb.man
--- xrdb.man	3 Nov 2004 00:22:58 -0000	1.2
+++ xrdb.man	27 May 2005 20:57:56 -0000
@@ -226,6 +226,10 @@
 should not run the input file through a preprocessor before loading it
 into properties.
 .TP 8
+.B -undef
+This option is passed to the C preprocessor if used. It prevents it from 
+predefining any system specific macros.
+.TP 8
 .B \-symbols
 This option indicates that the symbols that are defined for the preprocessor
 should be printed onto the standard output.