diff --git a/lib/bugsnag.rb b/lib/bugsnag.rb
index 178ce0efc..7d215b3d6 100644
--- a/lib/bugsnag.rb
+++ b/lib/bugsnag.rb
@@ -48,6 +48,12 @@ class << self
     def configure(validate_api_key=true)
       yield(configuration) if block_given?
 
+      # Create the session tracker if sessions are enabled to avoid the overhead
+      # of creating it on the first request. We skip this if we're not validating
+      # the API key as we use this internally before the user's configure block
+      # has run, so we don't know if sessions are enabled yet.
+      session_tracker if validate_api_key && configuration.auto_capture_sessions
+
       check_key_valid if validate_api_key
       check_endpoint_setup
 
diff --git a/lib/bugsnag/session_tracker.rb b/lib/bugsnag/session_tracker.rb
index d57e227c7..65c0f98a5 100644
--- a/lib/bugsnag/session_tracker.rb
+++ b/lib/bugsnag/session_tracker.rb
@@ -1,11 +1,9 @@
 require 'thread'
 require 'time'
 require 'securerandom'
-require 'concurrent'
 
 module Bugsnag
   class SessionTracker
-
     THREAD_SESSION = "bugsnag_session"
     SESSION_PAYLOAD_VERSION = "1.0"
     MUTEX = Mutex.new
@@ -27,6 +25,8 @@ def self.get_current_session
     ##
     # Initializes the session tracker.
     def initialize
+      require 'concurrent'
+
       @session_counts = Concurrent::Hash.new(0)
     end
 
@@ -139,4 +139,4 @@ def deliver(session_payload)
       Bugsnag::Delivery[Bugsnag.configuration.delivery_method].deliver(Bugsnag.configuration.session_endpoint, payload, Bugsnag.configuration, options)
     end
   end
-end
\ No newline at end of file
+end