diff --git a/icinga-app/icinga.cpp b/icinga-app/icinga.cpp
index 6b4af761438..5674a9ff243 100644
--- a/icinga-app/icinga.cpp
+++ b/icinga-app/icinga.cpp
@@ -447,6 +447,12 @@ static int Main()
 
 	Configuration::SetReadOnly(true);
 
+	if (!Configuration::ConcurrencyWasModified) {
+		Configuration::Concurrency = std::thread::hardware_concurrency();
+	}
+
+	Application::GetTP().Restart();
+
 	/* Ensure that all defined constants work in the way we expect them. */
 	HandleLegacyDefines();
 
diff --git a/lib/base/configuration.cpp b/lib/base/configuration.cpp
index d163937e2a7..31ae6048844 100644
--- a/lib/base/configuration.cpp
+++ b/lib/base/configuration.cpp
@@ -12,7 +12,8 @@ String Configuration::ApiBindHost;
 String Configuration::ApiBindPort{"5665"};
 bool Configuration::AttachDebugger{false};
 String Configuration::CacheDir;
-int Configuration::Concurrency{static_cast<int>(std::thread::hardware_concurrency())};
+int Configuration::Concurrency{1};
+bool Configuration::ConcurrencyWasModified{false};
 String Configuration::ConfigDir;
 String Configuration::DataDir;
 String Configuration::EventEngine;
@@ -101,6 +102,7 @@ int Configuration::GetConcurrency() const
 void Configuration::SetConcurrency(int val, bool suppress_events, const Value& cookie)
 {
 	HandleUserWrite("Concurrency", &Configuration::Concurrency, val, m_ReadOnly);
+	Configuration::ConcurrencyWasModified = true;
 }
 
 String Configuration::GetConfigDir() const
diff --git a/lib/base/configuration.hpp b/lib/base/configuration.hpp
index 560906596cc..a5aed01e8ea 100644
--- a/lib/base/configuration.hpp
+++ b/lib/base/configuration.hpp
@@ -118,6 +118,7 @@ class Configuration : public ObjectImpl<Configuration>
 	static bool AttachDebugger;
 	static String CacheDir;
 	static int Concurrency;
+	static bool ConcurrencyWasModified;
 	static String ConfigDir;
 	static String DataDir;
 	static String EventEngine;
diff --git a/lib/base/io-engine.cpp b/lib/base/io-engine.cpp
index 5dd3ee59cf6..056d3b9bfca 100644
--- a/lib/base/io-engine.cpp
+++ b/lib/base/io-engine.cpp
@@ -1,5 +1,6 @@
 /* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
 
+#include "base/configuration.hpp"
 #include "base/exception.hpp"
 #include "base/io-engine.hpp"
 #include "base/lazy-init.hpp"
@@ -84,10 +85,10 @@ boost::asio::io_context& IoEngine::GetIoContext()
 	return m_IoContext;
 }
 
-IoEngine::IoEngine() : m_IoContext(), m_KeepAlive(boost::asio::make_work_guard(m_IoContext)), m_Threads(decltype(m_Threads)::size_type(std::thread::hardware_concurrency() * 2u)), m_AlreadyExpiredTimer(m_IoContext)
+IoEngine::IoEngine() : m_IoContext(), m_KeepAlive(boost::asio::make_work_guard(m_IoContext)), m_Threads(decltype(m_Threads)::size_type(Configuration::Concurrency * 2u)), m_AlreadyExpiredTimer(m_IoContext)
 {
 	m_AlreadyExpiredTimer.expires_at(boost::posix_time::neg_infin);
-	m_CpuBoundSemaphore.store(std::thread::hardware_concurrency() * 3u / 2u);
+	m_CpuBoundSemaphore.store(Configuration::Concurrency * 3u / 2u);
 
 	for (auto& thread : m_Threads) {
 		thread = std::thread(&IoEngine::RunEventLoop, this);
diff --git a/lib/base/threadpool.cpp b/lib/base/threadpool.cpp
index 26787ab52a7..dc76e7b15bd 100644
--- a/lib/base/threadpool.cpp
+++ b/lib/base/threadpool.cpp
@@ -5,8 +5,7 @@
 
 using namespace icinga;
 
-ThreadPool::ThreadPool(size_t threads)
-	: m_Threads(threads), m_Pending(0)
+ThreadPool::ThreadPool() : m_Pending(0)
 {
 	Start();
 }
@@ -21,10 +20,15 @@ void ThreadPool::Start()
 	boost::unique_lock<decltype(m_Mutex)> lock (m_Mutex);
 
 	if (!m_Pool) {
-		m_Pool = decltype(m_Pool)(new boost::asio::thread_pool(m_Threads));
+		InitializePool();
 	}
 }
 
+void ThreadPool::InitializePool()
+{
+	m_Pool = decltype(m_Pool)(new boost::asio::thread_pool(Configuration::Concurrency * 2u));
+}
+
 void ThreadPool::Stop()
 {
 	boost::unique_lock<decltype(m_Mutex)> lock (m_Mutex);
@@ -34,3 +38,14 @@ void ThreadPool::Stop()
 		m_Pool = nullptr;
 	}
 }
+
+void ThreadPool::Restart()
+{
+	boost::unique_lock<decltype(m_Mutex)> lock (m_Mutex);
+
+	if (m_Pool) {
+		m_Pool->join();
+	}
+
+	InitializePool();
+}
diff --git a/lib/base/threadpool.hpp b/lib/base/threadpool.hpp
index af351cd7acb..d30fa694c9a 100644
--- a/lib/base/threadpool.hpp
+++ b/lib/base/threadpool.hpp
@@ -4,6 +4,7 @@
 #define THREADPOOL_H
 
 #include "base/atomic.hpp"
+#include "base/configuration.hpp"
 #include "base/exception.hpp"
 #include "base/logger.hpp"
 #include <cstddef>
@@ -36,11 +37,12 @@ class ThreadPool
 public:
 	typedef std::function<void ()> WorkFunction;
 
-	ThreadPool(size_t threads = std::thread::hardware_concurrency() * 2u);
+	ThreadPool();
 	~ThreadPool();
 
 	void Start();
 	void Stop();
+	void Restart();
 
 	/**
 	 * Appends a work item to the work queue. Work items will be processed in FIFO order.
@@ -89,8 +91,9 @@ class ThreadPool
 private:
 	boost::shared_mutex m_Mutex;
 	std::unique_ptr<boost::asio::thread_pool> m_Pool;
-	size_t m_Threads;
 	Atomic<uint_fast64_t> m_Pending;
+
+	void InitializePool();
 };
 
 }