diff --git a/tests/scripts/check-generated-files.sh b/tests/scripts/check-generated-files.sh
index 5e35be8..75730ba 100755
--- a/tests/scripts/check-generated-files.sh
+++ b/tests/scripts/check-generated-files.sh
@@ -65,24 +65,25 @@
     fi
 
     for FILE in "$@"; do
-        cp "$FILE" "$FILE.bak"
+        cp -p "$FILE" "$FILE.bak"
     done
 
     "$SCRIPT"
 
     # Compare the script output to the old files and remove backups
     for FILE in "$@"; do
-        if ! diff "$FILE" "$FILE.bak" >/dev/null 2>&1; then
+        if diff "$FILE" "$FILE.bak" >/dev/null 2>&1; then
+            # Move the original file back so that $FILE's timestamp doesn't
+            # change (avoids spurious rebuilds with make).
+            mv "$FILE.bak" "$FILE"
+        else
             echo "'$FILE' was either modified or deleted by '$SCRIPT'"
             if [ -z "$UPDATE" ]; then
                 exit 1
+            else
+                rm "$FILE.bak"
             fi
         fi
-        if [ -z "$UPDATE" ]; then
-            mv "$FILE.bak" "$FILE"
-        else
-            rm "$FILE.bak"
-        fi
     done
 
     if [ -n "$directory" ]; then