diff --git a/contrib/verify-commits/verify-commits.sh b/contrib/verify-commits/verify-commits.sh
index 40c9341445b..0052697cb90 100755
--- a/contrib/verify-commits/verify-commits.sh
+++ b/contrib/verify-commits/verify-commits.sh
@@ -3,9 +3,6 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-# Not technically POSIX-compliant due to use of "local", but almost every
-# shell anyone uses today supports it, so its probably fine
-
 DIR=$(dirname "$0")
 [ "/${DIR#/}" != "$DIR" ] && DIR=$(dirname "$(pwd)/$0")
 
@@ -16,14 +13,33 @@ VERIFIED_SHA512_ROOT=$(cat "${DIR}/trusted-sha512-root-commit")
 REVSIG_ALLOWED=$(cat "${DIR}/allow-revsig-commits")
 
 HAVE_FAILED=false
-IS_SIGNED () {
-	if [ $1 = $VERIFIED_ROOT ]; then
-		return 0;
+
+if [ x"$1" = "x" ]; then
+	CURRENT_COMMIT="HEAD"
+else
+	CURRENT_COMMIT="$1"
+fi
+
+if [ "${CURRENT_COMMIT#* }" != "$CURRENT_COMMIT" ]; then
+	echo "Commit must not contain spaces?" > /dev/stderr
+	exit 1
+fi
+
+VERIFY_TREE=0
+if [ x"$2" = "x--tree-checks" ]; then
+	VERIFY_TREE=1
+fi
+
+NO_SHA1=1
+PREV_COMMIT=""
+
+while true; do
+	if [ "$CURRENT_COMMIT" = $VERIFIED_ROOT ]; then
+		echo "There is a valid path from "$CURRENT_COMMIT" to $VERIFIED_ROOT where all commits are signed!"
+		exit 0;
 	fi
 
-	VERIFY_TREE=$2
-	NO_SHA1=$3
-	if [ $1 = $VERIFIED_SHA512_ROOT ]; then
+	if [ "$CURRENT_COMMIT" = $VERIFIED_SHA512_ROOT ]; then
 		if [ "$VERIFY_TREE" = "1" ]; then
 			echo "All Tree-SHA512s matched up to $VERIFIED_SHA512_ROOT" > /dev/stderr
 		fi
@@ -37,41 +53,51 @@ IS_SIGNED () {
 		export BITCOIN_VERIFY_COMMITS_ALLOW_SHA1=1
 	fi
 
-	if [ "${REVSIG_ALLOWED#*$1}" != "$REVSIG_ALLOWED" ]; then
+	if [ "${REVSIG_ALLOWED#*$CURRENT_COMMIT}" != "$REVSIG_ALLOWED" ]; then
 		export BITCOIN_VERIFY_COMMITS_ALLOW_REVSIG=1
 	else
 		export BITCOIN_VERIFY_COMMITS_ALLOW_REVSIG=0
 	fi
 
-	if ! git -c "gpg.program=${DIR}/gpg.sh" verify-commit $1 > /dev/null; then
-		return 1;
+	if ! git -c "gpg.program=${DIR}/gpg.sh" verify-commit "$CURRENT_COMMIT" > /dev/null; then
+		if [ "$PREV_COMMIT" != "" ]; then
+			echo "No parent of $PREV_COMMIT was signed with a trusted key!" > /dev/stderr
+			echo "Parents are:" > /dev/stderr
+			PARENTS=$(git show -s --format=format:%P $PREV_COMMIT)
+			for PARENT in $PARENTS; do
+				git show -s $PARENT > /dev/stderr
+			done
+		else
+			echo "$CURRENT_COMMIT was not signed with a trusted key!" > /dev/stderr
+		fi
+		exit 1
 	fi
 
-	# We set $4 to 1 on the first call, always verifying the top of the tree
-	if [ "$VERIFY_TREE" = 1 -o "$4" = "1" ]; then
+	# We always verify the top of the tree
+	if [ "$VERIFY_TREE" = 1 -o "$PREV_COMMIT" = "" ]; then
 		IFS_CACHE="$IFS"
 		IFS='
 '
-		for LINE in $(git ls-tree --full-tree -r $1); do
+		for LINE in $(git ls-tree --full-tree -r "$CURRENT_COMMIT"); do
 			case "$LINE" in
 				"12"*)
 					echo "Repo contains symlinks" > /dev/stderr
 					IFS="$IFS_CACHE"
-					return 1
+					exit 1
 					;;
 			esac
 		done
 		IFS="$IFS_CACHE"
 
 		FILE_HASHES=""
-		for FILE in $(git ls-tree --full-tree -r --name-only $1 | LC_ALL=C sort); do
-			HASH=$(git cat-file blob $1:"$FILE" | sha512sum | { read FIRST OTHER; echo $FIRST; } )
+		for FILE in $(git ls-tree --full-tree -r --name-only "$CURRENT_COMMIT" | LC_ALL=C sort); do
+			HASH=$(git cat-file blob "$CURRENT_COMMIT":"$FILE" | sha512sum | { read FIRST OTHER; echo $FIRST; } )
 			[ "$FILE_HASHES" != "" ] && FILE_HASHES="$FILE_HASHES"'
 '
 			FILE_HASHES="$FILE_HASHES$HASH  $FILE"
 		done
 		HASH_MATCHES=0
-		MSG="$(git show -s --format=format:%B $1 | tail -n1)"
+		MSG="$(git show -s --format=format:%B "$CURRENT_COMMIT" | tail -n1)"
 
 		case "$MSG  -" in
 			"Tree-SHA512: $(echo "$FILE_HASHES" | sha512sum)")
@@ -79,50 +105,15 @@ IS_SIGNED () {
 		esac
 
 		if [ "$HASH_MATCHES" = "0" ]; then
-			echo "Tree-SHA512 did not match for commit $1" > /dev/stderr
-			HAVE_FAILED=true
-			return 1
+			echo "Tree-SHA512 did not match for commit $CURRENT_COMMIT" > /dev/stderr
+			exit 1
 		fi
 	fi
 
-	local PARENTS
-	PARENTS=$(git show -s --format=format:%P $1)
+	PARENTS=$(git show -s --format=format:%P "$CURRENT_COMMIT")
 	for PARENT in $PARENTS; do
-		if IS_SIGNED $PARENT $VERIFY_TREE $NO_SHA1 0; then
-			return 0;
-		fi
+		PREV_COMMIT="$CURRENT_COMMIT"
+		CURRENT_COMMIT="$PARENT"
 		break
 	done
-	if ! "$HAVE_FAILED"; then
-		echo "No parent of $1 was signed with a trusted key!" > /dev/stderr
-		echo "Parents are:" > /dev/stderr
-		for PARENT in $PARENTS; do
-			git show -s $PARENT > /dev/stderr
-		done
-		HAVE_FAILED=true
-	fi
-	return 1;
-}
-
-if [ x"$1" = "x" ]; then
-	TEST_COMMIT="HEAD"
-else
-	TEST_COMMIT="$1"
-fi
-
-DO_CHECKOUT_TEST=0
-if [ x"$2" = "x--tree-checks" ]; then
-	DO_CHECKOUT_TEST=1
-fi
-
-IS_SIGNED "$TEST_COMMIT" "$DO_CHECKOUT_TEST" 1 1
-RES=$?
-if [ "$RES" = 1 ]; then
-	if ! "$HAVE_FAILED"; then
-		echo "$TEST_COMMIT was not signed with a trusted key!"
-	fi
-else
-	echo "There is a valid path from $TEST_COMMIT to $VERIFIED_ROOT where all commits are signed!"
-fi
-
-exit $RES
+done