Index: openacs-4/packages/wp-slim/www/serve-slide.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/wp-slim/www/serve-slide.tcl,v
diff -u -r1.12 -r1.13
--- openacs-4/packages/wp-slim/www/serve-slide.tcl	23 Jun 2015 16:19:30 -0000	1.12
+++ openacs-4/packages/wp-slim/www/serve-slide.tcl	27 Jun 2015 20:34:42 -0000	1.13
@@ -89,7 +89,7 @@
 
 # Figure out what the next slide link should be.    
 
-set next_sort_key [expr $sort_key + 1]
+set next_sort_key [expr {$sort_key + 1}]
 
 set found_slide [db_0or1row get_next_slide {
     select i.item_id as next_slide_item_id