Index: tcc4tcl.tcl
==================================================================
--- tcc4tcl.tcl
+++ tcc4tcl.tcl
@@ -36,20 +36,27 @@
 
 		array set $handle [list tcc $tcc_handle code "" type $type filename $output package $pkgName]
 
 		proc $handle {cmd args} [string map [list @@HANDLE@@ $handle] {
 			set handle {@@HANDLE@@}
+
 			if {$cmd == "go"} {
 				set args [list 0 {*}$args]
 			}
 
 			if {$cmd == "code"} {
 				set cmd "go"
 				set args [list 1 {*}$args]
 			}
 
-			uplevel 1 [list ::tcc4tcl::_$cmd $handle {*}$args]
+			set callcmd ::tcc4tcl::_$cmd
+
+			if {![info command $callcmd]} {
+				return -code error "unknown or ambiguous subcommand \"$cmd\": must be cproc, linktclcommand, code, tk, or go"
+			}
+
+			uplevel 1 [list $callcmd $handle {*}$args]
 		}]
 
 		return $handle
 	}