diff --git a/src/algorithm/geometry.hxx b/src/algorithm/geometry.hxx
index 1ca8ca5d9707cb5ec71549b1bb11607377ad3e82..b5f0ae688447c326bc761a5e9a3767df5a05f72a 100644
--- a/src/algorithm/geometry.hxx
+++ b/src/algorithm/geometry.hxx
@@ -194,6 +194,7 @@ namespace se3
     /// Append the geometry objects and geometry positions
     geomModel1.geometryObjects.insert(geomModel1.geometryObjects.end(),
         geomModel2.geometryObjects.begin(), geomModel2.geometryObjects.end());
+    geomModel1.ngeoms += nGeom2;
 
     /// 1. copy the collision pairs and update geomData1 accordingly.
     geomModel1.collisionPairs.reserve(nColPairs1 + nColPairs2 + nGeom1 * nGeom2);