Index: tcc4tcl.c
==================================================================
--- tcc4tcl.c
+++ tcc4tcl.c
@@ -30,11 +30,11 @@
 
 static void Tcc4tclErrorFunc(Tcl_Interp * interp, char * msg) {
 	Tcl_AppendResult(interp, msg, "\n", NULL);
 }
 
-static void Tcc4tclCCommandDeleteProc (ClientData cdata) {
+static void Tcc4tclCCommandDeleteProc(ClientData cdata) {
 	struct TclTCCState *ts;
 	TCCState *s ;
 
 	ts = (struct TclTCCState *) cdata;
 	s = ts->s;
@@ -41,10 +41,22 @@
 
 	ts->s = NULL;
 
 	ckfree((void *) ts);
 }
+
+static void Tcc4tclDeleteClientData(ClientData cdata) {
+	/*
+	 * ClientData is a Tcl_Obj*, that was passed in 
+	 * at command creation
+	 */
+	Tcl_Obj *cdata_o = (Tcl_Obj *)cdata;
+
+	if (cdata_o != NULL) {
+		Tcl_DecrRefCount(cdata_o);
+	}
+}
 
 static int Tcc4tclHandleCmd ( ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj * CONST objv[]){
 	Tcl_WideInt val;
 	Tcl_Obj *val_o;
 	void *val_p;
@@ -134,14 +146,15 @@
             val_p = (void *) val;
 
             tcc_add_symbol(s,Tcl_GetString(objv[2]), val_p); 
             return TCL_OK; 
         case TCC4TCL_COMMAND:
-            if (objc != 4) {
-                Tcl_WrongNumArgs(interp, 2, objv, "tclname cname");
+            if (objc != 4 && objc != 5) {
+                Tcl_WrongNumArgs(interp, 2, objv, "tclname cname ?clientData?");
                 return TCL_ERROR;
             }
+
             if (!ts->relocated) {     
                 if(tcc_relocate(s, TCC_RELOCATE_AUTO)!=0) {
                     Tcl_AppendResult(interp, "relocating failed", NULL);
                     return TCL_ERROR;
                 } else {
@@ -152,13 +165,21 @@
             val_p = tcc_get_symbol(s, Tcl_GetString(objv[3]));
             if (val_p == NULL) {
 		    Tcl_AppendResult(interp, "symbol '", Tcl_GetString(objv[3]),"' not found", NULL);
 		    return TCL_ERROR;
 	    }
+
+	    /* the ClientData */
+	    if (objc == 5) {
+		val_o = objv[4];
+		Tcl_IncrRefCount(val_o);
+	    } else {
+		val_o = NULL;
+	    }
 
             /*printf("symbol: %x\n",val); */
-            Tcl_CreateObjCommand(interp,Tcl_GetString(objv[2]),val_p,NULL,NULL);
+            Tcl_CreateObjCommand(interp, Tcl_GetString(objv[2]), val_p, val_o, Tcc4tclDeleteClientData);
             return TCL_OK;
         case TCC4TCL_COMPILE:
             if(ts->relocated == 1) {
                 Tcl_AppendResult(interp, "code already relocated, cannot compile more",NULL);
                 return TCL_ERROR;

Index: tcc4tcl.tcl
==================================================================
--- tcc4tcl.tcl
+++ tcc4tcl.tcl
@@ -55,14 +55,18 @@
 		}]
 
 		return $handle
 	}
 
-	proc _linktclcommand {handle cSymbol tclCommand} {
+	proc _linktclcommand {handle cSymbol args} {
 		upvar #0 $handle state
+		set argc [llength $args]
+		if {$argc != 1 && $argc != 2} {
+			return -code error "_linktclcommand handle cSymbol tclCommand ?clientData?"
+		}
 
-		lappend state(procs) $cSymbol $tclCommand
+		lappend state(procs) $cSymbol $args
 	}
 
 	proc _add_include_path {handle args} {
 		upvar #0 $handle state
 
@@ -91,11 +95,11 @@
 		set tclname [lindex $wrap 2]
 
 		append state(code) $wrapped "\n"
 		append state(code) $wrapper "\n"
 
-		lappend state(procs) $name $tclname
+		lappend state(procs) $name [list $tclname]
 	}
 
 	proc _cproc {handle name adefs rtype {body "#"}} {
 		upvar #0 $handle state
 
@@ -106,11 +110,11 @@
 		set tclname [lindex $wrap 2]
 
 		append state(code) $wrapped "\n"
 		append state(code) $wrapper "\n"
 
-		lappend state(procs) $name $tclname
+		lappend state(procs) $name [list $tclname]
 	}
 
 	proc _ccode {handle code} {
 		upvar #0 $handle state
 
@@ -404,21 +408,35 @@
 		switch -- $state(type) {
 			"memory" {
 				# No additional code needed
 				if {$outputOnly} {
 					if {[info exists state(procs)] && [llength $state(procs)] > 0} {
-						foreach {procname cname} $state(procs) {
-							append code "/* Immediate: Tcl_CreateObjCommand(interp, \"$procname\", $cname, NULL, NULL); */\n"
+						foreach {procname cname_obj} $state(procs) {
+							set cname [lindex $cname_obj 0]
+
+							if {[llength $cname_obj] > 1} {
+								set obj [lindex $cname_obj 1]
+							} else {
+								set obj "NULL"
+							}
+
+							append code "/* Immediate: Tcl_CreateObjCommand(interp, \"$procname\", $cname, $obj, Tcc4tclDeleteClientData); */\n"
 						}
 					}
 				}
 			}
 			"exe" - "dll" {
 				if {[info exists state(procs)] && [llength $state(procs)] > 0} {
 					append code "int _initProcs(Tcl_Interp *interp) \{\n"
 					
-					foreach {procname cname} $state(procs) {
+					foreach {procname cname_obj} $state(procs) {
+						set cname [lindex $cname_obj 0]
+
+						if {[llength $cname_obj] != 1} {
+							error "ClientData not supported in exe / dll mode"
+						}
+
 						append code "  Tcl_CreateObjCommand(interp, \"$procname\", $cname, NULL, NULL);\n"
 					}
 
 					append code "\}"
 				}
@@ -436,11 +454,17 @@
 				append code "    return TCL_ERROR;\n"
 				append code "  \}\n"
 				append code "#endif\n"
 
 				if {[info exists state(procs)] && [llength $state(procs)] > 0} {
-					foreach {procname cname} $state(procs) {
+					foreach {procname cname_obj} $state(procs) {
+						set cname [lindex $cname_obj 0]
+
+						if {[llength $cname_obj] != 1} {
+							error "ClientData not supported in exe / dll mode"
+						}
+
 						append code "  Tcl_CreateObjCommand(interp, \"$procname\", $cname, NULL, NULL);\n"
 					}
 				}
 
 				append code "  Tcl_PkgProvide(interp, \"$packageName\", \"$packageVersion\");\n"
@@ -484,12 +508,12 @@
 		switch -- $state(type) {
 			"memory" {
 				tcc compile $code
 
 				if {[info exists state(procs)] && [llength $state(procs)] > 0} {
-					foreach {procname cname} $state(procs) {
-						tcc command $procname $cname
+					foreach {procname cname_obj} $state(procs) {
+						tcc command $procname {*}$cname_obj
 					}
 				}
 			}
 
 			"package" - "dll" - "exe" {