diff --git a/doc/scripts/coverage.sh b/doc/scripts/coverage.sh
index e8befde..349c122 100755
--- a/doc/scripts/coverage.sh
+++ b/doc/scripts/coverage.sh
@@ -96,11 +96,14 @@ _usage()
 
 #main
 clean=0
-while getopts "cP:" name; do
+while getopts "cO:P:" name; do
 	case "$name" in
 		c)
 			clean=1
 			;;
+		O)
+			export "${OPTARG%%=*}"="${OPTARG#*=}"
+			;;
 		P)
 			#XXX ignored
 			;;