diff --git a/lib/prometheus/client/registry.rb b/lib/prometheus/client/registry.rb
index 4bf63aa4..0b2f6e9a 100644
--- a/lib/prometheus/client/registry.rb
+++ b/lib/prometheus/client/registry.rb
@@ -22,7 +22,7 @@ def register(metric)
         name = metric.name
 
         @mutex.synchronize do
-          if exist?(name.to_sym)
+          if @metrics.key?(name.to_sym)
             raise AlreadyRegisteredError, "#{name} has already been registered"
           end
           @metrics[name.to_sym] = metric
@@ -73,15 +73,15 @@ def histogram(name, docstring:, labels: [], preset_labels: {},
       end
 
       def exist?(name)
-        @metrics.key?(name)
+        @mutex.synchronize { @metrics.key?(name) }
       end
 
       def get(name)
-        @metrics[name.to_sym]
+        @mutex.synchronize { @metrics[name.to_sym] }
       end
 
       def metrics
-        @metrics.values
+        @mutex.synchronize { @metrics.values }
       end
     end
   end
diff --git a/spec/prometheus/client/registry_spec.rb b/spec/prometheus/client/registry_spec.rb
index 32727d00..3c4da190 100644
--- a/spec/prometheus/client/registry_spec.rb
+++ b/spec/prometheus/client/registry_spec.rb
@@ -33,10 +33,6 @@
       mutex = Mutex.new
       containers = []
 
-      def registry.exist?(*args)
-        super.tap { sleep(0.01) }
-      end
-
       Array.new(5) do
         Thread.new do
           result = begin