diff --git a/separate_rects.cpp b/separate_rects.cpp
index 3d76e53..9fd1ae4 100644
--- a/separate_rects.cpp
+++ b/separate_rects.cpp
@@ -85,7 +85,7 @@
   // our output set of non-overlapping rectangles. Based of the algorithm found
   // at: http://stackoverflow.com/a/2755498
 
-  if (in.size() > IdSet<TNum>::max_elements) {
+  if (in.size() > IdSet<TId>::max_elements) {
     return;
   }