diff --git a/ProDOS.pm b/ProDOS.pm
index 57649d9..1c1a3b4 100644
--- a/ProDOS.pm
+++ b/ProDOS.pm
@@ -1434,5 +1434,27 @@ sub copy_file {
   print "pofile=$pofile filename=$filename copy_filename=$copy_filename\n" if $debug;
 }
 
+#
+# Lock a file
+#
+sub lock_file {
+  my ($pofile, $filename, $dbg) = @_;
+
+  $debug = 1 if defined $dbg && $dbg;
+
+  print "pofile=$pofile filename=$filename\n" if $debug;
+}
+
+#
+# Unlock a file
+#
+sub unlock_file {
+  my ($pofile, $filename, $dbg) = @_;
+
+  $debug = 1 if defined $dbg && $dbg;
+
+  print "pofile=$pofile filename=$filename\n" if $debug;
+}
+
 1;
 
diff --git a/README b/README
index 90204e4..6665eb6 100644
--- a/README
+++ b/README
@@ -8,4 +8,6 @@ prowrite.pl -- started
 prorename.pl -- started
 prodelete.pl -- started
 procopy.pl -- started
+prolock.pl -- started
+prounlock.pl -- started
 
diff --git a/prolock.pl b/prolock.pl
new file mode 100644
index 0000000..913a44a
--- /dev/null
+++ b/prolock.pl
@@ -0,0 +1,33 @@
+#!/usr/bin/perl -w
+
+#
+# prolock.pl:
+#
+# Utility to 'lock' a file on an Apple II ProDOS .po disk image.
+#
+# 20190228 LSH
+#
+
+use strict;
+
+use ProDOS;
+
+my $debug = 0;
+
+while (defined $ARGV[0] && $ARGV[0] =~ /^-/) {
+  # Debug
+  if ($ARGV[0] eq '-d') {
+    $debug = 1;
+    shift;
+  } else {
+    die "Unknown command line argument $ARGV[0]\n";
+  }
+}
+
+my $pofile = shift or die "Must supply .po filename\n";
+my $filename = shift or die "Must supply filename (on disk image)\n";
+
+lock_file($pofile, $filename, $debug);
+
+1;
+
diff --git a/prounlock.pl b/prounlock.pl
new file mode 100644
index 0000000..9e64394
--- /dev/null
+++ b/prounlock.pl
@@ -0,0 +1,33 @@
+#!/usr/bin/perl -w
+
+#
+# prounlock.pl:
+#
+# Utility to 'unlock' a file on an Apple II ProDOS .po disk image.
+#
+# 20190228 LSH
+#
+
+use strict;
+
+use ProDOS;
+
+my $debug = 0;
+
+while (defined $ARGV[0] && $ARGV[0] =~ /^-/) {
+  # Debug
+  if ($ARGV[0] eq '-d') {
+    $debug = 1;
+    shift;
+  } else {
+    die "Unknown command line argument $ARGV[0]\n";
+  }
+}
+
+my $pofile = shift or die "Must supply .po filename\n";
+my $filename = shift or die "Must supply filename (on disk image)\n";
+
+unlock_file($pofile, $filename, $debug);
+
+1;
+