diff --git a/pdb/app.pl b/pdb/app.pl
index 4acca8daa9..3294a06ba3 100644
--- a/pdb/app.pl
+++ b/pdb/app.pl
@@ -472,11 +472,12 @@ g_param_spec_uint ("$name",
 CODE
     }
     elsif ($pdbtype eq 'guide') {
+        $min = exists $arg->{none_ok} ? 0 : 1,
 	$pspec = <<CODE;
 g_param_spec_uint ("$name",
                    "$nick",
                    "$blurb",
-                   1, G_MAXUINT32, 1,
+                   $min, G_MAXUINT32, $min,
                    $flags)
 CODE
     }
diff --git a/pdb/groups/image_guides.pdb b/pdb/groups/image_guides.pdb
index c748a070b5..444193ffb6 100644
--- a/pdb/groups/image_guides.pdb
+++ b/pdb/groups/image_guides.pdb
@@ -138,6 +138,7 @@ HELP
     @inargs = (
 	{ name => 'image', type => 'image',
 	  desc => 'The image' },
+        # TODO: this should be changed to type 'guide' with none_ok => 1 when we can break API.
 	{ name => 'guide', type => '0 <= int32', default => 1, no_validate => 1,
 	  desc => 'The ID of the current guide (0 if first invocation)' }
     );
diff --git a/pdb/lib.pl b/pdb/lib.pl
index 438539f4f4..8fe10e54f6 100644
--- a/pdb/lib.pl
+++ b/pdb/lib.pl
@@ -140,7 +140,7 @@ sub generate_fun {
             $annotate   = " (array length=$retarg_len)";
         }
 
-        if (exists $retarg->{none_ok} && $type ne 'sample_point') {
+        if (exists $retarg->{none_ok} && $type ne 'sample_point' && $type ne 'guide') {
             $annotate .= " (nullable)";
         }
 
@@ -294,7 +294,7 @@ sub generate_fun {
             $n_annotations++;
         }
 
-        if (exists $_->{none_ok} && $type ne 'sample_point') {
+        if (exists $_->{none_ok} && $type ne 'sample_point' && $type ne 'guide') {
             $argdesc .= " (nullable)";
             $n_annotations++;
         }