diff --git a/GNUmakefile b/GNUmakefile
index 7138f4f43..9ba526a7b 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -14,7 +14,7 @@ export SDL_VIDEODRIVER = dummy
 SOURCE_PORT_NAME = chocolate-doom
 SOURCE_PORT := $(shell which $(SOURCE_PORT_NAME) || echo missing_source_port)
 DOOMOPTS = -mb 16 -nodraw -noblit -nosound \
-           -noautoload -nogui -nograbmouse
+           -noautoload -nogui -nograbmouse -nofullscreen
 
 ALL_DEMOS = $(patsubst %,demos/%,$(shell cat demos.txt))
 OUTPUTS = $(subst .lmp,.txt,$(subst demos/,output/,$(ALL_DEMOS)))