diff --git a/src/spectator/expectations/expectation.cr b/src/spectator/expectations/expectation.cr
index f7bd03b..d073a5a 100644
--- a/src/spectator/expectations/expectation.cr
+++ b/src/spectator/expectations/expectation.cr
@@ -25,7 +25,7 @@ module Spectator::Expectations
     end
 
     def failure_message
-      @match_data.as(Matchers::FailedMatchData).failure_message
+      failure_message?.not_nil!
     end
 
     def values?
@@ -33,7 +33,7 @@ module Spectator::Expectations
     end
 
     def values
-      @match_data.as(Matchers::FailedMatchData).values
+      values?.not_nil!
     end
 
     # Creates the JSON representation of the expectation.