diff --git a/contrib/gbdiff.bash b/contrib/gbdiff.bash
index 0a06172d..2772a0bb 100755
--- a/contrib/gbdiff.bash
+++ b/contrib/gbdiff.bash
@@ -23,51 +23,51 @@
 # SOFTWARE.
 
 STATE=0
-diff <(xxd $1) <(xxd $2) | while read -r LINE; do
-	if [ $STATE -eq 0 ]; then
+diff <(xxd "$1") <(xxd "$2") | while read -r LINE; do
+	if [[ $STATE -eq 0 ]]; then
 		# Discard first line (line info)
 		STATE=1
-	elif [ "$LINE" = '---' ]; then
+	elif [[ "$LINE" = '---' ]]; then
 		# Separator between files switches states
-		echo $LINE
+		echo "$LINE"
 		STATE=3
 	elif grep -Eq '^[0-9]+(,[0-9]+)?[cd][0-9]+(,[0-9]+)?' <<< "$LINE"; then
 		# Line info resets the whole thing
 		STATE=1
-	elif [ $STATE -eq 1  -o  $STATE -eq 3 ]; then
+	elif [[ $STATE -eq 1  ||  $STATE -eq 3 ]]; then
 		# Compute the GB address from the ROM offset
 		OFS=$(cut -d ' ' -f 2 <<< "$LINE" | tr -d ':')
 		BANK=$((0x$OFS / 0x4000))
-		ADDR=$((0x$OFS % 0x4000 + ($BANK != 0) * 0x4000))
+		ADDR=$((0x$OFS % 0x4000 + (BANK != 0) * 0x4000))
 		# Try finding the preceding symbol closest to the diff
-		if [ $STATE -eq 1 ]; then
+		if [[ $STATE -eq 1 ]]; then
 			STATE=2
 			SYMFILE=${1%.*}.sym
 		else
 			STATE=4
 			SYMFILE=${2%.*}.sym
 		fi
-		EXTRA=$(if [ -f "$SYMFILE" ]; then
+		EXTRA=$(if [[ -f "$SYMFILE" ]]; then
 			# Read the sym file for such a symbol
 			# Ignore comment lines, only pick matching bank
 			# (The bank regex ignores comments already, make `cut` and `tr` process less lines)
-			grep -Ei $(printf "^%02x:" $BANK) "$SYMFILE" |
+			grep -Ei "$(printf "^%02x:" $BANK)" "$SYMFILE" |
 			 cut -d ';' -f 1 |
 			 tr -d "\r" |
 			 while read -r SYMADDR SYM; do
 				SYMADDR=$((0x${SYMADDR#*:}))
-				if [ $SYMADDR -le $ADDR ]; then
-					printf " (%s+%#x)\n" "$SYM" $(($ADDR - $SYMADDR))
+				if [[ $SYMADDR -le $ADDR ]]; then
+					printf " (%s+%#x)\n" "$SYM" $((ADDR - SYMADDR))
 				fi
 			# TODO: assumes sorted sym files
 			done | tail -n 1
 		fi)
-		printf "%02x:%04x %s\n" $BANK $ADDR $EXTRA
+		printf "%02x:%04x %s\n" $BANK $ADDR "$EXTRA"
 	fi
-	if [ $STATE -eq 2  -o  $STATE -eq 4 ]; then
+	if [[ $STATE -eq 2  ||  $STATE -eq 4 ]]; then
 		OFS=$(cut -d ' ' -f 2 <<< "$LINE" | tr -d ':')
 		BANK=$((0x$OFS / 0x4000))
-		ADDR=$((0x$OFS % 0x4000 + ($BANK != 0) * 0x4000))
+		ADDR=$((0x$OFS % 0x4000 + (BANK != 0) * 0x4000))
 		printf "%s %02x:%04x: %s\n" "${LINE:0:1}" $BANK $ADDR "${LINE#*: }"
 	fi
 done