diff --git a/src/swd/intensity_data.cr b/src/swd/intensity_data.cr
index 183f576..bd23ca6 100644
--- a/src/swd/intensity_data.cr
+++ b/src/swd/intensity_data.cr
@@ -9,13 +9,13 @@ class SWD
     # Return the marginal intensity for a country when provided an ISO
     # code
     def self.marginal_by_iso(iso : String) : Float64?
-      MARGINAL_INTENSITY_BY_ISO_CODE[iso]
+      MARGINAL_INTENSITY_BY_ISO_CODE[iso] if MARGINAL_INTENSITY_BY_ISO_CODE.has_key? iso
     end
 
     # Return the average intensity for a country when provided an ISO
     # code
     def self.average_by_iso(iso : String) : Float64?
-      AVERAGE_INTENSITY_BY_ISO_CODE[iso]
+      AVERAGE_INTENSITY_BY_ISO_CODE[iso] if AVERAGE_INTENSITY_BY_ISO_CODE.has_key? iso
     end
 
     def self.by_iso(iso : String, type : Symbol = :marginal) : Float64?