diff --git a/.local/bin/run0edit b/.local/bin/run0edit
index 0909e39..8a8b033 100755
--- a/.local/bin/run0edit
+++ b/.local/bin/run0edit
@@ -30,7 +30,7 @@ make_editable_copy() {
     orig_file="$1"
     tempfile="$2"
 
-    try_command cp "${orig_file}" "${tempfile}"
+    try_command cp -- "${orig_file}" "${tempfile}"
 }
 
 elevate_permissions() {
@@ -45,15 +45,21 @@ update_file() {
     tempfile="$1"
     orig_file="$2"
 
-    try_command mv --force "${tempfile}" "${orig_file}"
+    try_command mv --force -- "${tempfile}" "${orig_file}"
 }
 
 clean_tempfiles() {
     tempfile="$1"
 
-    rm --force "${tempfile}" "${tempfile}.orig"
+    rm --force -- "${tempfile}" "${tempfile}.orig"
 }
 
+if [ "$#" -ne "1" ]; then
+    echo "Expected exactly one input file. Usage:" 1>&2
+    echo "   $0 FILE" 1>&2
+    exit 1;
+fi
+
 editor_cmd="$(default_editor)"
 echo "Editing using the command \"${editor_cmd}\""