diff --git a/core/lib/spree/event/subscriber_registry.rb b/core/lib/spree/event/subscriber_registry.rb
index 1d9572563f5..4e3529e1c01 100644
--- a/core/lib/spree/event/subscriber_registry.rb
+++ b/core/lib/spree/event/subscriber_registry.rb
@@ -5,10 +5,10 @@ module Event
     class SubscriberRegistry
       def initialize
         @registry = {}
+        @semaphore = Mutex.new
       end
 
       def register(subscriber)
-        # thread safe?
         registry[subscriber.name] ||= {}
       end
 
@@ -29,26 +29,22 @@ def activate_subscriber(subscriber)
         return unless registry[subscriber.name]
 
         subscriber.event_actions.each do |event_action, event_name|
-          deactivate_subscriber(subscriber, event_action)
+          @semaphore.synchronize do
+            unsafe_deactivate_subscriber(subscriber, event_action)
 
-          subscription = Spree::Event.subscribe(event_name) { |event| subscriber.send(event_action, event) }
+            subscription = Spree::Event.subscribe(event_name) { |event| subscriber.send(event_action, event) }
 
-          # deprecated mappings, to be removed when Solidus 2.10 is not supported anymore:
-          subscriber.send("#{event_action}_handler=", subscription)
+            # deprecated mappings, to be removed when Solidus 2.10 is not supported anymore:
+            subscriber.send("#{event_action}_handler=", subscription)
 
-          registry[subscriber.name][event_action] = subscription
+            registry[subscriber.name][event_action] = subscription
+          end
         end
       end
 
-      def deactivate_subscriber(subscriber, event_action_name=nil)
-        to_unsubscribe = Array.wrap(event_action_name || subscriber.event_actions.keys)
-
-        to_unsubscribe.each do |event_action|
-          if (subscription = registry.dig(subscriber.name, event_action))
-            Spree::Event.unsubscribe(subscription)
-
-            registry[subscriber.name].delete(event_action)
-          end
+      def deactivate_subscriber(subscriber, event_action_name = nil)
+        @semaphore.synchronize do
+          unsafe_deactivate_subscriber(subscriber, event_action_name)
         end
       end
 
@@ -79,6 +75,18 @@ def require_subscriber_files
           Rails.root.glob(pattern) { |c| require_dependency(c.to_s) }
         end
       end
+
+      def unsafe_deactivate_subscriber(subscriber, event_action_name = nil)
+        to_unsubscribe = Array.wrap(event_action_name || subscriber.event_actions.keys)
+
+        to_unsubscribe.each do |event_action|
+          if (subscription = registry.dig(subscriber.name, event_action))
+            Spree::Event.unsubscribe(subscription)
+
+            registry[subscriber.name].delete(event_action)
+          end
+        end
+      end
     end
   end
 end