diff --git a/src/simulation/Simulation.cpp b/src/simulation/Simulation.cpp
index 6477fd4af..f92affb1a 100644
--- a/src/simulation/Simulation.cpp
+++ b/src/simulation/Simulation.cpp
@@ -4156,7 +4156,8 @@ void Simulation::update_particles()//doesn't update the particles themselves, bu
 					// To make particles collide correctly when inside these elements, these elements must not overwrite an existing pmap entry from particles inside them
 					if (!pmap[y][x] || (t!=PT_INVIS && t!= PT_FILT))
 						pmap[y][x] = t|(i<<8);
-					pmap_count[y][x]++;
+					if (t!=PT_THDR)
+						pmap_count[y][x]++;
 				}
 			}
 			lastPartUsed = i;