diff --git a/howso/mda_weight.amlg b/howso/mda_weight.amlg
index dda5a2af..2dd59c67 100644
--- a/howso/mda_weight.amlg
+++ b/howso/mda_weight.amlg
@@ -504,7 +504,8 @@
 							(zip
 								features
 								(map
-									(lambda (get (current_value) feature_index))
+									;convert any nulls to 0s
+									(lambda (+ (or (get (current_value) feature_index))) )
 									mda_matrix
 								)
 							)