diff --git a/lib/mini_profiler/storage/redis_store.rb b/lib/mini_profiler/storage/redis_store.rb
index 5e4f615f..b1ab2e20 100644
--- a/lib/mini_profiler/storage/redis_store.rb
+++ b/lib/mini_profiler/storage/redis_store.rb
@@ -33,7 +33,7 @@ def load(id)
 
       def set_unviewed(user, id)
         key = user_key(user)
-        if redis.exists(prefixed_id(id))
+        if redis.exists?(prefixed_id(id))
           expire_at = Process.clock_gettime(Process::CLOCK_MONOTONIC).to_i + redis.ttl(prefixed_id(id))
           redis.zadd(key, expire_at, id)
         end
@@ -44,7 +44,7 @@ def set_all_unviewed(user, ids)
         key = user_key(user)
         redis.del(key)
         ids.each do |id|
-          if redis.exists(prefixed_id(id))
+          if redis.exists?(prefixed_id(id))
             expire_at = Process.clock_gettime(Process::CLOCK_MONOTONIC).to_i + redis.ttl(prefixed_id(id))
             redis.zadd(key, expire_at, id)
           end
diff --git a/rack-mini-profiler.gemspec b/rack-mini-profiler.gemspec
index 8c89d81a..e0a9f7d6 100644
--- a/rack-mini-profiler.gemspec
+++ b/rack-mini-profiler.gemspec
@@ -33,7 +33,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'activerecord', '~> 3.0'
   s.add_development_dependency 'dalli'
   s.add_development_dependency 'rspec', '~> 3.6.0'
-  s.add_development_dependency 'redis'
+  s.add_development_dependency 'redis', '~> 4.2.1'
   s.add_development_dependency 'sassc'
   s.add_development_dependency 'flamegraph'
   s.add_development_dependency 'rubocop'