diff --git a/server/json-adapter.cc b/server/json-adapter.cc
index 4984fd9..9c71dab 100644
--- a/server/json-adapter.cc
+++ b/server/json-adapter.cc
@@ -258,7 +258,7 @@ void JsonAdapter::prepare_run(const std::string& address, unsigned start_port, u
 {
 	check_guard();
 	// delayed after constructor, so virtual functions are working:
-	i->session_registry.reset(new SessionRegistry(messageToSend ? messageToSend : this->getMessageToSend(), this->getInjectSyncEvent()));
+	i->session_registry.reset(new SessionRegistry(messageToSend ? messageToSend : this->getMessageToSend(), this->getInjectSyncEvent(), i->client_session_timeout));
 	
 	for(unsigned short port = start_port; port<=end_port; ++port)
 	{
diff --git a/server/server_version.cc b/server/server_version.cc
index 5f7e41e..d22be12 100644
--- a/server/server_version.cc
+++ b/server/server_version.cc
@@ -76,7 +76,8 @@ static const std::string VersionName =
 //	"(42) Gotha"; // JSON-152: 2-parameter version of pollForEvents().
 //	"(43) Wandersleben"; // JSON-153 passphrase support. *sigh*
 //	"(44) Neudietendorf"; // replace my own sync thread code by libpEpAdapter's implementation.
-	"(45) Kreuz Erfurt"; // fix of context-saved function parameters that would cause trouble when >1 request is processed in parallel.
+//	"(45) Kreuz Erfurt"; // fix of context-saved function parameters that would cause trouble when >1 request is processed in parallel.
+	"(46) Erfurt-West";  // JSON-156: delete client cached values after timeout.
 
 } // end of anonymous namespace
 ////////////////////////////////////////////////////////////////////////////
diff --git a/server/session_registry.cc b/server/session_registry.cc
index 2a56167..ef4e11c 100644
--- a/server/session_registry.cc
+++ b/server/session_registry.cc
@@ -10,6 +10,8 @@ PEP_SESSION SessionRegistry::get(std::thread::id tid, const std::string& client_
 {
 	Lock L(_mtx);
 	
+	update_last_use(client_id);
+	
 	auto q = m.find(tid);
 	if(q != m.end())
 	{
@@ -69,6 +71,7 @@ void SessionRegistry::add_to_cache(const std::string& client_id, const std::stri
 	Lock L(_mtx);
 	Log.debug("add_to_cache(\"%s\", \"%s\")", client_id.c_str(), fn_name.c_str());
 	cache[client_id][fn_name] = func;
+	update_last_use(client_id);
 }
 
 
@@ -83,3 +86,23 @@ std::string SessionRegistry::to_string() const
 	}
 	return ss.str();
 }
+
+
+void SessionRegistry::update_last_use(const std::string& client_id)
+{
+	const auto now = std::chrono::system_clock::now();
+	const auto too_old = now - std::chrono::seconds(client_timeout);
+	last_use[client_id] = now;
+	
+	// TODO: replace by C++20 std::erase_if()
+	for(auto q = last_use.begin(); q != last_use.end(); /* no increment here */ )
+	{
+		if(q->second < too_old)
+		{
+			cache.erase( q->first );
+			q = last_use.erase(q);
+		}else{
+			++q;
+		}
+	}
+}
diff --git a/server/session_registry.hh b/server/session_registry.hh
index d9e1fce..c44ac2c 100644
--- a/server/session_registry.hh
+++ b/server/session_registry.hh
@@ -1,6 +1,7 @@
 #ifndef JSON_ADAPTER_SESSION_REGISTRY_HH
 #define JSON_ADAPTER_SESSION_REGISTRY_HH
 
+#include <chrono>
 #include <map>
 #include <mutex>
 #include <thread>
@@ -11,10 +12,11 @@
 class SessionRegistry
 {
 public:
-	SessionRegistry(messageToSend_t _mts, inject_sync_event_t _ise)
+	SessionRegistry(messageToSend_t _mts, inject_sync_event_t _ise, int _client_timeout)
 	: mts{_mts}
 	, ise{_ise}
 	, Log{"SR"}
+	, client_timeout{_client_timeout} // in seconds
 	{}
 	
 	// calls "init" for the given thread if no PEP_SESSION exists, yet for the given thread
@@ -36,16 +38,23 @@ private:
 	std::map<std::thread::id, PEP_SESSION> m;
 	messageToSend_t      mts;
 	inject_sync_event_t  ise;
-	Logger Log;
+	Logger               Log;
+	int       client_timeout; // in seconds
 	
+	// function name -> functor
 	typedef
 	std::map<std::string, std::function<void(PEP_SESSION)>> cache_per_client_t;
 	
+	// key=client_id
 	std::map<std::string, cache_per_client_t> cache;
 	
+	std::map<std::string, std::chrono::time_point<std::chrono::system_clock> > last_use;
+	
 	typedef std::recursive_mutex     Mutex;
 	typedef std::unique_lock<Mutex>  Lock;
 	mutable Mutex  _mtx;
+	
+	void update_last_use(const std::string& client_id);
 };
 
 #endif // JSON_ADAPTER_SESSION_REGISTRY_HH