diff --git a/src/test/regress/bin/diff b/src/test/regress/bin/diff
index 1cbb0d227..5fcddbf53 100755
--- a/src/test/regress/bin/diff
+++ b/src/test/regress/bin/diff
@@ -18,7 +18,7 @@ file2="${@:(-1):1}"
 # filename of the expected file as the test name. We can have multiple
 # expected files for a single test with _0, _1, ... suffixes.
 # So for the test name, we also strip the additional suffix.
-test=$(basename $file1 .out | sed -E "s/_[0-9]+$//")
+test=$(basename "$file1" .out | sed -E "s/_[0-9]+$//")
 args=${@:1:$#-2}
 BASEDIR=$(dirname "$0")
 
@@ -33,16 +33,11 @@ fi
 if test -z "${VANILLATEST:-}"
 then
 	touch "$file1"  # when adding a new test the expected file does not exist
-	sed -Ef $BASEDIR/normalize.sed < $file1 > "$file1.modified"
-	mv "$file1" "$file1.unmodified"
-	mv "$file1.modified" "$file1"
+	sed -Ef $BASEDIR/normalize.sed < "$file1" > "$file1.modified"
 	sed -Ef $BASEDIR/normalize.sed < "$file2" > "$file2.modified"
-	mv "$file2" "$file2.unmodified"
-	mv "$file2.modified" "$file2"
-	$DIFF -w $args $file1 $file2
-	exitcode=$?
-	exit $exitcode
+	"$DIFF" -w $args "$file1.modified" "$file2.modified" | diff-filter
+	exit ${PIPESTATUS[0]}
 else
-	exec $DIFF -w $args $file1 $file2
+	exec "$DIFF" -w $args "$file1" "$file2"
 fi
 
diff --git a/src/test/regress/bin/diff-filter b/src/test/regress/bin/diff-filter
new file mode 100755
index 000000000..092dee629
--- /dev/null
+++ b/src/test/regress/bin/diff-filter
@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+
+"""
+diff-filter denormalizes diff output by having lines beginning with ' ' or '+'
+come from file2's unmodified version.
+"""
+
+def main():
+	from sys import stdin, stdout
+
+	for line in stdin:
+		if line.startswith('+++ '):
+			tab = line.rindex('\t')
+			fname = line[4:tab]
+			file2 = iter(open(fname.replace('.modified', '')))
+			file2line = 1
+			stdout.write(line)
+		elif line.startswith('@@ '):
+			idx_start = line.index('+') + 1
+			idx_end = idx_start + 1
+			while line[idx_end].isdigit():
+				idx_end += 1
+			linenum = int(line[idx_start:idx_end])
+			while file2line < linenum:
+				next(file2)
+				file2line += 1
+			stdout.write(line)
+		elif line.startswith(' '):
+			stdout.write(' ')
+			stdout.write(next(file2))
+			file2line += 1
+		elif line.startswith('+'):
+			stdout.write('+')
+			stdout.write(next(file2))
+			file2line += 1
+		else:
+			stdout.write(line)
+
+main()