diff --git a/lib/sidekiq/redis_connection.rb b/lib/sidekiq/redis_connection.rb
index 4d5664d5..064c2137 100644
--- a/lib/sidekiq/redis_connection.rb
+++ b/lib/sidekiq/redis_connection.rb
@@ -115,27 +115,20 @@ module Sidekiq
         # REDIS_PROVIDER=MY_REDIS_URL
         # and Sidekiq will find your custom URL variable with no custom
         # initialization code at all.
+        #
         p = ENV['REDIS_PROVIDER']
         if p && p =~ /\:/
-          Sidekiq.logger.error <<-EOM
+          raise <<-EOM
+REDIS_PROVIDER should be set to the name of the variable which contains the Redis URL, not a URL itself.
+Platforms like Heroku will sell addons that publish a *_URL variable.  You need to tell Sidekiq with REDIS_PROVIDER, e.g.:
 
-#################################################################################
-
-REDIS_PROVIDER should be set to the **name** of the variable which contains the Redis URL, not a URL itself.
-Platforms like Heroku sell addons that publish a *_URL variable.  You tell Sidekiq with REDIS_PROVIDER, e.g.:
-
-  REDIS_PROVIDER=REDISTOGO_URL
-  REDISTOGO_URL=redis://somehost.example.com:6379/4
-
-Use REDIS_URL if you wish to point Sidekiq to a URL directly.
-
-This configuration error will crash starting in Sidekiq 5.3.
-
-#################################################################################
+REDIS_PROVIDER=REDISTOGO_URL
+REDISTOGO_URL=redis://somehost.example.com:6379/4
 EOM
         end
+
         ENV[
-          ENV['REDIS_PROVIDER'] || 'REDIS_URL'
+          p || 'REDIS_URL'
         ]
       end
 
diff --git a/test/test_redis_connection.rb b/test/test_redis_connection.rb
index 2af17676..0110144b 100644
--- a/test/test_redis_connection.rb
+++ b/test/test_redis_connection.rb
@@ -223,6 +223,18 @@ class TestRedisConnection < Minitest::Test
     end
 
     describe "with REDIS_PROVIDER set" do
+      it "rejects URLs in REDIS_PROVIDER" do
+        uri = 'redis://sidekiq-redis-provider:6379/0'
+
+        ENV['REDIS_PROVIDER'] = uri
+
+        #assert_raises RuntimeError do
+          Sidekiq::RedisConnection.__send__(:determine_redis_provider)
+        #end
+
+        ENV['REDIS_PROVIDER'] = nil
+      end
+
       it "sets connection URI to the provider" do
         uri = 'redis://sidekiq-redis-provider:6379/0'
         provider = 'SIDEKIQ_REDIS_PROVIDER'