diff --git a/tesseract_collision/core/include/tesseract_collision/core/types.h b/tesseract_collision/core/include/tesseract_collision/core/types.h
index 486b553057e..4f80ff4c02a 100644
--- a/tesseract_collision/core/include/tesseract_collision/core/types.h
+++ b/tesseract_collision/core/include/tesseract_collision/core/types.h
@@ -296,7 +296,7 @@ class ContactResultMap
   std::stringstream getCollisionSummary() const
   {
     std::stringstream ss;
-    std::map<KeyType, int> collision_counts;
+    std::map<KeyType, std::size_t> collision_counts;
     std::map<KeyType, double> closest_distances;
 
     // Initialize distances map with max values