diff --git a/compare.jq b/compare.jq
index 326b4de..88a366e 100644
--- a/compare.jq
+++ b/compare.jq
@@ -2,7 +2,7 @@
 #
 # Where .[0] is the new value, and .[1] is the old value
 def calc_change($key):
-	. as $input | $input[0][$key] - $input[1][$key];
+	. as $input | ($input[0][$key] // 0) - ($input[1][$key] // 0);
 
 # Calculate the change in percentage for multiple keys
 #