diff --git a/lib/signature.rb b/lib/signature.rb
index 57b5867..19d16da 100644
--- a/lib/signature.rb
+++ b/lib/signature.rb
@@ -223,6 +223,8 @@ def validate_signature!(token)
 
       # Constant time string comparison
       def identical?(a, b)
+        return true if a.nil? && b.nil?
+        return false if a.nil? || b.nil?
         return false unless a.bytesize == b.bytesize
         a.bytes.zip(b.bytes).reduce(0) { |memo, (a, b)| memo += a ^ b } == 0
       end