diff --git a/kimimaro/trace.py b/kimimaro/trace.py
index a09208a..a4c8807 100644
--- a/kimimaro/trace.py
+++ b/kimimaro/trace.py
@@ -352,6 +352,8 @@ def compute_pdrf(dbf_max, pdrf_scale, pdrf_exponent, DBF, DAF):
   # provide trickle of gradient so open spaces don't collapse
   max_daf = np.max(DAF)
   if max_daf != 0:
+    print(max_daf)
+    print(DAF)
     PDRF += DAF * (1 / max_daf)
 
   return np.asfortranarray(PDRF)