diff --git a/lib/sidekiq/client.rb b/lib/sidekiq/client.rb
index 26e9be7e..e7cb2d9d 100644
--- a/lib/sidekiq/client.rb
+++ b/lib/sidekiq/client.rb
@@ -25,6 +25,8 @@ module Sidekiq
       @chain
     end
 
+    attr_accessor :redis_pool
+
     # Sidekiq::Client normally uses the default Redis pool but you may
     # pass a custom ConnectionPool if you want to shard your
     # Sidekiq jobs across several Redis instances (for scalability
@@ -32,8 +34,13 @@ module Sidekiq
     #
     #   Sidekiq::Client.new(ConnectionPool.new { Redis.new })
     #
-    def initialize(redis_pool = Sidekiq.redis_pool)
-      @redis_pool = redis_pool
+    # Generally this is only needed for very large Sidekiq installs processing
+    # more than thousands jobs per second.  I do not recommend sharding unless
+    # you truly cannot scale any other way (e.g. splitting your app into smaller apps).
+    # Some features, like the API, do not support sharding: they are designed to work
+    # against a single Redis instance only.
+    def initialize(redis_pool=nil)
+      @redis_pool = redis_pool || Thread.current[:sidekiq_via_pool] || Sidekiq.redis_pool
     end
 
     ##
@@ -88,6 +95,29 @@ module Sidekiq
       pushed ? payloads.collect { |payload| payload['jid'] } : nil
     end
 
+    # Allows sharding of jobs across any number of Redis instances.  All jobs
+    # defined within the block will use the given Redis connection pool.
+    #
+    #   pool = ConnectionPool.new { Redis.new }
+    #   Sidekiq::Client.via(pool) do
+    #     SomeWorker.perform_async(1,2,3)
+    #     SomeOtherWorker.perform_async(1,2,3)
+    #   end
+    #
+    # Generally this is only needed for very large Sidekiq installs processing
+    # more than thousands jobs per second.  I do not recommend sharding unless
+    # you truly cannot scale any other way (e.g. splitting your app into smaller apps).
+    # Some features, like the API, do not support sharding: they are designed to work
+    # against a single Redis instance.
+    def self.via(pool)
+      raise ArgumentError, "No pool given" if pool.nil?
+      raise RuntimeError, "Sidekiq::Client.via is not re-entrant" if x = Thread.current[:sidekiq_via_pool] && x != pool
+      Thread.current[:sidekiq_via_pool] = pool
+      yield
+    ensure
+      Thread.current[:sidekiq_via_pool] = nil
+    end
+
     class << self
 
       def default
diff --git a/lib/sidekiq/worker.rb b/lib/sidekiq/worker.rb
index 85398923..82f4d164 100644
--- a/lib/sidekiq/worker.rb
+++ b/lib/sidekiq/worker.rb
@@ -34,25 +34,6 @@ module Sidekiq
       Sidekiq.logger
     end
 
-    # Allows sharding of jobs across any number of Redis instances.  All jobs
-    # defined within the block will use the given Redis connection pool.
-    #
-    #   pool = ConnectionPool.new { Redis.new }
-    #   Sidekiq::Worker.via(pool) do
-    #     SomeWorker.perform_async(1,2,3)
-    #     SomeOtherWorker.perform_async(1,2,3)
-    #   end
-    #
-    # Generally this is only needed for very large Sidekiq installs processing
-    # more than thousands jobs per second.
-    def self.via(pool)
-      raise ArgumentError, "No pool given" if pool.nil?
-      Thread.current[:sidekiq_via_pool] = pool
-      yield
-    ensure
-      Thread.current[:sidekiq_via_pool] = nil
-    end
-
     module ClassMethods
 
       def perform_async(*args)
diff --git a/test/test_client.rb b/test/test_client.rb
index f6a078d7..ecdfffa9 100644
--- a/test/test_client.rb
+++ b/test/test_client.rb
@@ -250,11 +250,18 @@ class TestClient < Sidekiq::Test
     it 'allows #via to point to different Redi' do
       conn = MiniTest::Mock.new
       conn.expect(:multi, [0, 1])
-      default = Sidekiq::Client.redis_pool
-      Sidekiq::Client.via(ConnectionPool.new(size: 1) { conn }) do
+      default = Sidekiq::Client.new.redis_pool
+      sharded_pool = ConnectionPool.new(size: 1) { conn }
+      Sidekiq::Client.via(sharded_pool) do
         CWorker.perform_async(1,2,3)
+        assert_equal sharded_pool, Sidekiq::Client.new.redis_pool
+        assert_raises RuntimeError do
+          Sidekiq::Client.via(default) do
+            # nothing
+          end
+        end
       end
-      assert_equal default, Sidekiq::Client.redis_pool
+      assert_equal default, Sidekiq::Client.new.redis_pool
       conn.verify
     end
     it 'allows Resque helpers to point to different Redi' do