diff --git a/lib/raven/interfaces/message.rb b/lib/raven/interfaces/message.rb
index 2b5fa5a89..2427893c1 100644
--- a/lib/raven/interfaces/message.rb
+++ b/lib/raven/interfaces/message.rb
@@ -10,7 +10,7 @@ def initialize(*arguments)
     end
 
     def unformatted_message
-      message % params
+      params.nil? ? message : message % params
     end
 
     def self.sentry_alias
diff --git a/spec/raven/interface_spec.rb b/spec/raven/interface_spec.rb
index a6cc4f597..5f607eb4c 100644
--- a/spec/raven/interface_spec.rb
+++ b/spec/raven/interface_spec.rb
@@ -24,3 +24,10 @@ class TestInterface < Raven::Interface
     expect(interface.to_hash).to eq(:some_attr => "test")
   end
 end
+
+describe Raven::MessageInterface do
+  it "supports invalid format string message when params is not defined" do
+    interface = Raven::MessageInterface.new(:params => nil, :message => "test '%'")
+    expect(interface.unformatted_message).to eq("test '%'")
+  end
+end