diff --git a/compiler/options.pas b/compiler/options.pas
index b131897aaa..80465c80bd 100644
--- a/compiler/options.pas
+++ b/compiler/options.pas
@@ -603,8 +603,13 @@ begin
 
            'd' :
              if more <> '' then
-               def_system_macro(more);
-
+               begin
+                 l:=Pos(':=',more);
+                 if l>0 then
+                   set_system_compvar(Copy(more,1,l-1),Copy(more,l+2,255))                  
+                 else
+                   def_system_macro(more);
+               end;
            'D' :
              begin
                include(initglobalswitches,cs_link_deffile);
diff --git a/compiler/symtable.pas b/compiler/symtable.pas
index a22ac9e458..658f851acf 100644
--- a/compiler/symtable.pas
+++ b/compiler/symtable.pas
@@ -227,6 +227,7 @@ interface
     {Name can be given in any case (it will be converted to upper case).}
     procedure def_system_macro(const name : string);
     procedure set_system_macro(const name, value : string);
+    procedure set_system_compvar(const name, value : string);
     procedure undef_system_macro(const name : string);
 
 {*** symtable stack ***}
@@ -2321,6 +2322,37 @@ implementation
          mac.defined:=true;
       end;
 
+    procedure set_system_compvar(const name, value : string);
+      var
+        mac : tmacro;
+        s: string;
+      begin
+        if name = '' then
+          internalerror(2004121201);
+         s:= upper(name);
+         mac:=tmacro(search_macro(s));
+         if not assigned(mac) then
+           begin
+             mac:=tmacro.create(s);
+             mac.is_compiler_var:=true;
+             if macrosymtablestack.symtabletype=localmacrosymtable then
+               macrosymtablestack.insert(mac)
+             else
+               macrosymtablestack.next.insert(mac)
+           end
+         else
+           begin
+             mac.is_compiler_var:=true;
+             if assigned(mac.buftext) then
+               freemem(mac.buftext,mac.buflen);
+           end;
+         Message2(parser_c_macro_set_to,mac.name,value);
+         mac.buflen:=length(value);
+         getmem(mac.buftext,mac.buflen);
+         move(value[1],mac.buftext^,mac.buflen);
+         mac.defined:=true;
+      end;
+
     procedure undef_system_macro(const name : string);
       var
         mac : tmacro;