diff --git a/lib/cli/daemoncommand.cpp b/lib/cli/daemoncommand.cpp
index 28ab0459d..1fca07b5c 100644
--- a/lib/cli/daemoncommand.cpp
+++ b/lib/cli/daemoncommand.cpp
@@ -3,6 +3,7 @@
 #include "cli/daemoncommand.hpp"
 #include "cli/daemonutility.hpp"
 #include "remote/apilistener.hpp"
+#include "remote/configobjectslock.hpp"
 #include "remote/configobjectutility.hpp"
 #include "config/configcompiler.hpp"
 #include "config/configcompilercontext.hpp"
@@ -801,6 +802,10 @@ int DaemonCommand::Run(const po::variables_map& vm, const std::vector<std::strin
 			sd_notify(0, "RELOADING=1");
 #endif /* HAVE_SYSTEMD */
 
+			// The old process is still active, yet.
+			// Its config changes would not be visible to the new one after config load.
+			ConfigObjectsExclusiveLock lock;
+
 			pid_t nextWorker = StartUnixWorker(configs);
 
 			switch (nextWorker) {
diff --git a/lib/icinga/apiactions.cpp b/lib/icinga/apiactions.cpp
index 1e3fe851f..25d2b0852 100644
--- a/lib/icinga/apiactions.cpp
+++ b/lib/icinga/apiactions.cpp
@@ -12,6 +12,7 @@
 #include "icinga/clusterevents.hpp"
 #include "remote/apiaction.hpp"
 #include "remote/apilistener.hpp"
+#include "remote/configobjectslock.hpp"
 #include "remote/filterutility.hpp"
 #include "remote/pkiutility.hpp"
 #include "remote/httputility.hpp"
@@ -254,6 +255,12 @@ Dictionary::Ptr ApiActions::AcknowledgeProblem(const ConfigObject::Ptr& object,
 		return ApiActions::CreateResult(409, (service ? "Service " : "Host ") + checkable->GetName() + " is already acknowledged.");
 	}
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		return ApiActions::CreateResult(503, "Icinga is reloading.");
+	}
+
 	Comment::AddComment(checkable, CommentAcknowledgement, HttpUtility::GetLastParameter(params, "author"),
 		HttpUtility::GetLastParameter(params, "comment"), persistent, timestamp, sticky == AcknowledgementSticky);
 	checkable->AcknowledgeProblem(HttpUtility::GetLastParameter(params, "author"),
@@ -272,6 +279,12 @@ Dictionary::Ptr ApiActions::RemoveAcknowledgement(const ConfigObject::Ptr& objec
 			"Cannot remove acknowledgement for non-existent checkable object "
 			+ object->GetName() + ".");
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		return ApiActions::CreateResult(503, "Icinga is reloading.");
+	}
+
 	String removedBy (HttpUtility::GetLastParameter(params, "author"));
 
 	checkable->ClearAcknowledgement(removedBy);
@@ -297,6 +310,12 @@ Dictionary::Ptr ApiActions::AddComment(const ConfigObject::Ptr& object,
 		timestamp = HttpUtility::GetLastParameter(params, "expiry");
 	}
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		return ApiActions::CreateResult(503, "Icinga is reloading.");
+	}
+
 	String commentName = Comment::AddComment(checkable, CommentUser,
 		HttpUtility::GetLastParameter(params, "author"),
 		HttpUtility::GetLastParameter(params, "comment"), false, timestamp);
@@ -316,6 +335,12 @@ Dictionary::Ptr ApiActions::AddComment(const ConfigObject::Ptr& object,
 Dictionary::Ptr ApiActions::RemoveComment(const ConfigObject::Ptr& object,
 	const Dictionary::Ptr& params)
 {
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		return ApiActions::CreateResult(503, "Icinga is reloading.");
+	}
+
 	auto author (HttpUtility::GetLastParameter(params, "author"));
 	Checkable::Ptr checkable = dynamic_pointer_cast<Checkable>(object);
 
@@ -388,6 +413,12 @@ Dictionary::Ptr ApiActions::ScheduleDowntime(const ConfigObject::Ptr& object,
 		}
 	}
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		return ApiActions::CreateResult(503, "Icinga is reloading.");
+	}
+
 	Downtime::Ptr downtime = Downtime::AddDowntime(checkable, author, comment, startTime, endTime,
 		fixed, triggerName, duration);
 	String downtimeName = downtime->GetName();
@@ -500,6 +531,12 @@ Dictionary::Ptr ApiActions::ScheduleDowntime(const ConfigObject::Ptr& object,
 Dictionary::Ptr ApiActions::RemoveDowntime(const ConfigObject::Ptr& object,
 	const Dictionary::Ptr& params)
 {
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		return ApiActions::CreateResult(503, "Icinga is reloading.");
+	}
+
 	auto author (HttpUtility::GetLastParameter(params, "author"));
 	Checkable::Ptr checkable = dynamic_pointer_cast<Checkable>(object);
 
diff --git a/lib/remote/createobjecthandler.cpp b/lib/remote/createobjecthandler.cpp
index c01b23641..598eeec3b 100644
--- a/lib/remote/createobjecthandler.cpp
+++ b/lib/remote/createobjecthandler.cpp
@@ -1,6 +1,7 @@
 /* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
 
 #include "remote/createobjecthandler.hpp"
+#include "remote/configobjectslock.hpp"
 #include "remote/configobjectutility.hpp"
 #include "remote/httputility.hpp"
 #include "remote/jsonrpcconnection.hpp"
@@ -94,6 +95,13 @@ bool CreateObjectHandler::HandleRequest(
 	if (params)
 		verbose = HttpUtility::GetLastParameter(params, "verbose");
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		HttpUtility::SendJsonError(response, params, 503, "Icinga is reloading");
+		return true;
+	}
+
 	/* Object creation can cause multiple errors and optionally diagnostic information.
 	 * We can't use SendJsonError() here.
 	 */
diff --git a/lib/remote/deleteobjecthandler.cpp b/lib/remote/deleteobjecthandler.cpp
index 2edb0e455..a4fd98d9a 100644
--- a/lib/remote/deleteobjecthandler.cpp
+++ b/lib/remote/deleteobjecthandler.cpp
@@ -1,6 +1,7 @@
 /* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
 
 #include "remote/deleteobjecthandler.hpp"
+#include "remote/configobjectslock.hpp"
 #include "remote/configobjectutility.hpp"
 #include "remote/httputility.hpp"
 #include "remote/filterutility.hpp"
@@ -66,6 +67,13 @@ bool DeleteObjectHandler::HandleRequest(
 	bool cascade = HttpUtility::GetLastParameter(params, "cascade");
 	bool verbose = HttpUtility::GetLastParameter(params, "verbose");
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		HttpUtility::SendJsonError(response, params, 503, "Icinga is reloading");
+		return true;
+	}
+
 	ArrayData results;
 
 	bool success = true;
diff --git a/lib/remote/modifyobjecthandler.cpp b/lib/remote/modifyobjecthandler.cpp
index cc008b90c..d9a215f5f 100644
--- a/lib/remote/modifyobjecthandler.cpp
+++ b/lib/remote/modifyobjecthandler.cpp
@@ -1,6 +1,7 @@
 /* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
 
 #include "remote/modifyobjecthandler.hpp"
+#include "remote/configobjectslock.hpp"
 #include "remote/httputility.hpp"
 #include "remote/filterutility.hpp"
 #include "remote/apiaction.hpp"
@@ -77,6 +78,13 @@ bool ModifyObjectHandler::HandleRequest(
 	if (params)
 		verbose = HttpUtility::GetLastParameter(params, "verbose");
 
+	ConfigObjectsSharedLock lock (std::try_to_lock);
+
+	if (!lock) {
+		HttpUtility::SendJsonError(response, params, 503, "Icinga is reloading");
+		return true;
+	}
+
 	ArrayData results;
 
 	for (const ConfigObject::Ptr& obj : objs) {