diff --git a/lib/frost/signing_key.rb b/lib/frost/signing_key.rb
index d3b4693..82b8c9b 100644
--- a/lib/frost/signing_key.rb
+++ b/lib/frost/signing_key.rb
@@ -18,7 +18,7 @@ def initialize(scalar, group = ECDSA::Group::Secp256k1)
 
     # Generate signing key.
     # @param [ECDSA::Group] group Group of elliptic curve.
-    def self.generate(group = ECDSA::Group::Secp256k1)
+    def self.generate(group)
       scalar = 1 + SecureRandom.random_number(group.order - 1)
       SigningKey.new(scalar, group)
     end
diff --git a/spec/signing_key_spec.rb b/spec/signing_key_spec.rb
index a3b10bc..89bdbe0 100644
--- a/spec/signing_key_spec.rb
+++ b/spec/signing_key_spec.rb
@@ -5,7 +5,7 @@
   describe "#new" do
     context 'valid key range' do
       it do
-        expect{described_class.generate}.not_to raise_error
+        expect{described_class.generate(ECDSA::Group::Secp256k1)}.not_to raise_error
       end
     end
     context 'invalid key range' do