diff --git a/lib/floe/workflow/choice_rule/data.rb b/lib/floe/workflow/choice_rule/data.rb
index fb626fd5a..e1daf5f04 100644
--- a/lib/floe/workflow/choice_rule/data.rb
+++ b/lib/floe/workflow/choice_rule/data.rb
@@ -4,6 +4,17 @@ module Floe
   class Workflow
     class ChoiceRule
       class Data < Floe::Workflow::ChoiceRule
+        COMPARE_KEYS = %w[IsNull IsPresent IsNumeric IsString IsBoolean IsTimestamp String Numeric Boolean Timestamp].freeze
+
+        attr_reader :compare_key
+
+        def initialize(*)
+          super
+          @compare_key = payload.keys.detect { |key| key.match?(/^(#{COMPARE_KEYS.join("|")})/) }
+
+          raise Floe::InvalidWorkflowError, "Data-test Expression Choice Rule must have a compare key" if @compare_key.nil?
+        end
+
         def true?(context, input)
           lhs = variable_value(context, input)
           rhs = compare_value(context, input)
@@ -80,10 +91,6 @@ def is_timestamp?(value) # rubocop:disable Naming/PredicateName
           false
         end
 
-        def compare_key
-          @compare_key ||= payload.keys.detect { |key| key.match?(/^(IsNull|IsPresent|IsNumeric|IsString|IsBoolean|IsTimestamp|String|Numeric|Boolean|Timestamp)/) }
-        end
-
         def compare_value(context, input)
           compare_key.end_with?("Path") ? Path.value(payload[compare_key], context, input) : payload[compare_key]
         end
diff --git a/spec/workflow/choice_rule_spec.rb b/spec/workflow/choice_rule_spec.rb
index b08209ada..763582a4d 100644
--- a/spec/workflow/choice_rule_spec.rb
+++ b/spec/workflow/choice_rule_spec.rb
@@ -75,6 +75,15 @@
         end
       end
 
+      context "with a missing compare key" do
+        let(:payload) { {"Variable" => "$.foo", "Next" => "FirstMatchState"} }
+        let(:input) { {"foo" => "bar"} }
+
+        it "raises an exception" do
+          expect { subject }.to raise_exception(RuntimeError, "Data-test Expression Choice Rule must have a compare key")
+        end
+      end
+
       context "with IsNull" do
         let(:payload) { {"Variable" => "$.foo", "IsNull" => true} }