diff --git a/src/powder.c b/src/powder.c
index 1c06e4dcf..0c46daa4f 100644
--- a/src/powder.c
+++ b/src/powder.c
@@ -1646,7 +1646,7 @@ void update_particles_i(pixel *vid, int start, int inc)
 						if ((r>>8)>=NPART || !r)
 							continue;
 						rt = r&0xFF;
-						if (rt&&ptypes[rt].hconduct&&(rt!=PT_HSWC||parts[r>>8].life==10)
+						if (rt&&ptypes[rt].hconduct&&ptypes[rt].weight>0&&(rt!=PT_HSWC||parts[r>>8].life==10)
 						        &&(t!=PT_FILT||(rt!=PT_BRAY&&rt!=PT_BIZR&&rt!=PT_BIZRG))
 						        &&(rt!=PT_FILT||(t!=PT_BRAY&&t!=PT_PHOT&&t!=PT_BIZR&&t!=PT_BIZRG)))
 						{
@@ -1657,8 +1657,7 @@ void update_particles_i(pixel *vid, int start, int inc)
 						}
 					}
 
-					pt = parts[i].temp = (c_heat+parts[i].temp*96.645/ptypes[t].hconduct*ptypes[t].weight)
-						/(c_Cm+96.645/ptypes[t].hconduct*ptypes[t].weight);
+					pt = parts[i].temp = (c_heat+parts[i].temp*96.645/ptypes[t].hconduct*ptypes[t].weight)/(c_Cm+96.645/ptypes[t].hconduct*ptypes[t].weight);
 					for (j=0; j<8; j++)
 					{
 						parts[surround_hconduct[j]].temp = pt;