diff --git a/lib/openmsx/share/scripts/headless.tcl b/lib/openmsx/share/scripts/headless.tcl
index f8ed69e..cccadaa 100644
--- a/lib/openmsx/share/scripts/headless.tcl
+++ b/lib/openmsx/share/scripts/headless.tcl
@@ -28,7 +28,8 @@
 # Sets CPU speed to relative from normal but only when throttle is on.
 #
 
-set boot_env_renderer_type 0
+set headless_renderer_type 0
+set headless_renderer_done 0
 
 proc headless_exit {} {
 	after time 1 "exit 0"
@@ -38,19 +39,24 @@ proc headless_exit {} {
 proc headless_show_gui {} {
 	global renderer
 	global throttle
-	global boot_env_renderer_type
-	if {$boot_env_renderer_type != 0} {
-		after time 1 "set renderer $boot_env_renderer_type"
+	global headless_renderer_type
+	global headless_renderer_done
+	if {$headless_renderer_done != 0} {
+		return "Requested GUI already showing"
+	}
+	if {$headless_renderer_type != 0} {
+		after time 1 "set renderer $headless_renderer_type"
 		set throttle on
+		set headless_renderer_done 1
 	} else {
 		puts stderr "error: Requested show gui but env.RENDERER is missing."
 		exit 1
 	}
-	return "Requested GUI with $boot_env_renderer_type"
+	return "Requested GUI with $headless_renderer_type"
 }
 
 if {[info exists ::env(RENDERER)] && ([string trim $::env(RENDERER)] != "")} {
-	set boot_env_renderer_type [string trim $::env(RENDERER)]
+	set headless_renderer_type [string trim $::env(RENDERER)]
 }
 
 if {[info exists ::env(HEADLESS)] && ([string trim $::env(HEADLESS)] != "on")} {