diff --git a/lib/jwt/x5c_key_finder.rb b/lib/jwt/x5c_key_finder.rb
index 26540855..a98abc45 100644
--- a/lib/jwt/x5c_key_finder.rb
+++ b/lib/jwt/x5c_key_finder.rb
@@ -40,7 +40,7 @@ def build_store(root_certificates, crls)
     end
 
     def parse_certificates(x5c_header_or_certificates)
-      if x5c_header_or_certificates.all? { |obj| obj.is_a?(OpenSSL::X509::Certificate) }
+      if x5c_header_or_certificates.all?(OpenSSL::X509::Certificate)
         x5c_header_or_certificates
       else
         x5c_header_or_certificates.map do |encoded|