diff --git a/data/tools/unit_tree/update-wmlunits b/data/tools/unit_tree/update-wmlunits
index 47d3a0fb60b8..1c0f2de88f3e 100755
--- a/data/tools/unit_tree/update-wmlunits
+++ b/data/tools/unit_tree/update-wmlunits
@@ -9,8 +9,10 @@ set -e -u
 # must run from the correct directory
 DIR="$(dirname $0)"
 
+EXTRA_ADDON_OPTIONS=${EXTRA_ADDON_OPTIONS:-}
+EXTRA_WMLUNITS_OPTIONS=${EXTRA_WMLUNITS_OPTIONS:-}
 TIMEOUT=${TIMEOUT:-20}
-SOURCES=/usr/src/wesnoth
+SOURCES=${SOURCES:-/usr/src/wesnoth}
 ADDONS=$DIR/addons
 EXE=$DIR/wesnoth
 CONFIG=$DIR/config
@@ -18,7 +20,7 @@ SRC=$SOURCES/$VERSION
 DATA=$SRC
 LOG=$DIR/logs
 TMPOUT=$DIR/output
-OUT="elias@192.168.1.2:/srv/www/html/units/$VERSION"
+OUT=${OUT:-"elias@192.168.1.2:/srv/www/html/units/$VERSION"}
 TRANS=$DIR/translations
 BUILD=$DIR/build
 # always using the master version
@@ -47,9 +49,11 @@ TRAVIS=1 TRAVIS_OS_NAME=Linux scons -Y "$SRC" --option-cache="$BUILD/.scons-opti
 rm -f $DIR/overview.txt
 
 echo DOWNLOADING
-$TOOLS/wesnoth_addon_manager -p $PORT -d '.*' -c $ADDONS > $LOG/wesnoth_addon_manager.txt 2>&1
+$TOOLS/wesnoth_addon_manager -p $PORT -d '.*' -c $ADDONS $EXTRA_ADDON_OPTIONS > $LOG/wesnoth_addon_manager.txt 2>&1
 echo WORKING
-python3 -u $TOOLS/wmlunits -t $TRANS -D $DATA -o $TMPOUT -w $EXE -C $CONFIG -a $ADDONS -L $DIR/overview.txt -B $DIR/overview.txt -T $TIMEOUT > $LOG/wmlunits.txt 2>&1
+python3 -u $TOOLS/wmlunits -t $TRANS -D $DATA -o $TMPOUT -w $EXE \
+    -C $CONFIG -a $ADDONS -L $DIR/overview.txt -B $DIR/overview.txt \
+    -T $TIMEOUT $EXTRA_WMLUNITS_OPTIONS > $LOG/wmlunits.txt 2>&1
 test -f $TMPOUT/mainline/en_US/mainline.html
 test -f $TMPOUT/'pics/core$images$units$woses$wose.png'
 rsync -vaz --delete $TMPOUT/ $OUT > $LOG/rsync.txt 2>&1
diff --git a/data/tools/wmlunits b/data/tools/wmlunits
index 45ecb3b4fa78..1cf6e12d47fd 100755
--- a/data/tools/wmlunits
+++ b/data/tools/wmlunits
@@ -185,7 +185,7 @@ def list_contents():
         dependency_eras = list(mainline_eras)
         for d in get_all_dependencies(addon):
             dinfo = search(batchlist, d)
-            for era in dinfo["eras"]:
+            for era in dinfo.get("eras", []):
                 dependency_eras.append(era["id"])
         return dependency_eras
 
@@ -346,7 +346,7 @@ def list_contents():
         except Exception as e:
             ef = open(logname, "w")
             ef.write("<INTERNAL ERROR>\n")
-            ef.write(str(e))
+            ef.write(repr(e))
             ef.write("</INTERNAL ERROR>\n")
             ef.close()
             sys.stdout.write("failed\n")