diff --git a/qpdf/qtest/qpdf/diff-encrypted b/qpdf/qtest/qpdf/diff-encrypted
index d730536..ac5428c 100755
--- a/qpdf/qtest/qpdf/diff-encrypted
+++ b/qpdf/qtest/qpdf/diff-encrypted
@@ -1,7 +1,7 @@
 #!/bin/sh
-lines=$(expr + $(diff $1 $2 | egrep '^[<>]' | egrep -v '(Date|InstanceID)' | wc -l))
+lines=$(expr 0 + $(diff "$1" "$2" | egrep '^[<>]' | egrep -v '(Date|InstanceID)' | wc -l))
 if [ "$lines" = "0" ]; then
    echo okay
 else
-   diff -a -U 0 $1 $2
+   diff -a -U 0 "$1" "$2"
 fi
diff --git a/qpdf/qtest/qpdf/diff-ignore-ID-version b/qpdf/qtest/qpdf/diff-ignore-ID-version
index e6b3347..72def44 100755
--- a/qpdf/qtest/qpdf/diff-ignore-ID-version
+++ b/qpdf/qtest/qpdf/diff-ignore-ID-version
@@ -1,8 +1,8 @@
 #!/bin/sh
-lines=$(expr + $(diff $1 $2 | egrep '^[<>]' | \
+lines=$(expr 0 + $(diff "$1" "$2" | egrep '^[<>]' | \
         egrep -v '/ID' | egrep -v '%PDF-' | wc -l))
 if [ "$lines" = "0" ]; then
    echo okay
 else
-   diff -a -U 0 $1 $2
+   diff -a -U 0 "$1" "$2"
 fi