diff --git a/lib/omniauth/strategies/oauth2.rb b/lib/omniauth/strategies/oauth2.rb
index 1588926..f0b929e 100644
--- a/lib/omniauth/strategies/oauth2.rb
+++ b/lib/omniauth/strategies/oauth2.rb
@@ -105,7 +105,7 @@ def callback_phase # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexi
       def pkce_authorize_params
         return {} unless options.pkce
 
-        options.pkce_verifier = SecureRandom.hex(64)
+        options.pkce_verifier ||= SecureRandom.hex(64)
 
         # NOTE: see https://tools.ietf.org/html/rfc7636#appendix-A
         {