diff --git a/CHANGELOG.md b/CHANGELOG.md
index 97d2123..a810835 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -36,6 +36,7 @@ keys and public keys
 - Fixed the return type of `Nostr::Crypto#decrypt_text` when given an invalid ciphertext
 - Fixed the RBS type of `Nostr::Filter#to_h`, `Nostr::Filter#e` and `Nostr::Filter#p`
 - Fixed the RBS types of `EventEmitter` and `EventMachine::Channel`
+- Fixed the generation of private keys
 
 ## [0.4.0] - 2023-02-25
 
diff --git a/lib/nostr/keygen.rb b/lib/nostr/keygen.rb
index d8bd226..761e5fd 100644
--- a/lib/nostr/keygen.rb
+++ b/lib/nostr/keygen.rb
@@ -47,7 +47,7 @@ module Nostr
     # @return [PrivateKey] A 32-bytes hex-encoded private key.
     #
     def generate_private_key
-      hex_value = (SecureRandom.random_number(group.order - 1) + 1).to_s(16)
+      hex_value = (SecureRandom.random_number(group.order - 1) + 1).to_s(16).rjust(64, '0')
       PrivateKey.new(hex_value)
     end