diff --git a/sub_extract_convert b/sub_extract_convert
index 97b8921..42d0b73 100755
--- a/sub_extract_convert
+++ b/sub_extract_convert
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # usage: $scriptname $files $output_sub_format
 output_sub_format=${@: -1}
-for i in $@
+for i in "$@"
 do
   if [ ! -e "$i" ];
   then
@@ -9,16 +9,16 @@ do
   	continue
   fi
   index=$(ffprobe -v 8 -show_streams -select_streams s "$i" | grep index | cut --delimiter="=" -f 2)
-  if [ -z $index ];
+  if [ -z "$index" ];
   then
   	echo "No subtitle streams found."
   	exit
   fi
   ffprobe -v 8 -show_streams -select_streams "$i"
   filename=${i%.*}
-  mkvextract "$i" tracks $index:"${filename}.en.ass"
-  if [ ! -z $1 ];
+  mkvextract "$i" tracks "$index":"${filename}.en.ass"
+  if [ -n "$1" ];
   then
-  	subtitleedit /convert "${filename}.en.ass" $output_sub_format 2>/dev/null | grep --color=none ass
+  	subtitleedit /convert "${filename}.en.ass" "$output_sub_format" 2>/dev/null | grep --color=none ass
   fi
 done
\ No newline at end of file