diff --git a/lib/nostr/errors/invalid_signature_type_error.rb b/lib/nostr/errors/invalid_signature_type_error.rb
index bc389c9..07b1015 100644
--- a/lib/nostr/errors/invalid_signature_type_error.rb
+++ b/lib/nostr/errors/invalid_signature_type_error.rb
@@ -11,6 +11,6 @@ module Nostr
     # @example
     #   InvalidSignatureTypeError.new
     #
-    def initialize = super('Invalid signature type')
+    def initialize = super('Invalid signature type. It must be a string with lowercase hexadecimal characters.')
   end
 end
diff --git a/spec/nostr/errors/invalid_signature_type_error_spec.rb b/spec/nostr/errors/invalid_signature_type_error_spec.rb
index d38db3d..2fb004e 100644
--- a/spec/nostr/errors/invalid_signature_type_error_spec.rb
+++ b/spec/nostr/errors/invalid_signature_type_error_spec.rb
@@ -7,7 +7,7 @@ RSpec.describe Nostr::InvalidSignatureTypeError do
     let(:error) { described_class.new }
 
     it 'builds a useful error message' do
-      expect(error.message).to eq('Invalid signature type')
+      expect(error.message).to eq('Invalid signature type. It must be a string with lowercase hexadecimal characters.')
     end
   end
 end
diff --git a/spec/nostr/signature_spec.rb b/spec/nostr/signature_spec.rb
index da20b36..f49513f 100644
--- a/spec/nostr/signature_spec.rb
+++ b/spec/nostr/signature_spec.rb
@@ -15,7 +15,7 @@ RSpec.describe Nostr::Signature do
       it 'raises an InvalidSignatureTypeError' do
         expect { described_class.new(1234) }.to raise_error(
           Nostr::InvalidSignatureTypeError,
-          'Invalid signature type'
+          'Invalid signature type. It must be a string with lowercase hexadecimal characters.'
         )
       end
     end