diff --git a/lib/icinga/host.cpp b/lib/icinga/host.cpp
index c9b4e7ea1..4ce3458ae 100644
--- a/lib/icinga/host.cpp
+++ b/lib/icinga/host.cpp
@@ -49,6 +49,8 @@ void Host::Start(void)
 	Array::Ptr groups = GetGroups();
 
 	if (groups) {
+		ObjectLock olock(groups);
+
 		BOOST_FOREACH(const String& name, groups) {
 			HostGroup::Ptr hg = HostGroup::GetByName(name);
 
@@ -70,6 +72,8 @@ void Host::Stop(void)
 	Array::Ptr groups = GetGroups();
 
 	if (groups) {
+		ObjectLock olock(groups);
+
 		BOOST_FOREACH(const String& name, groups) {
 			HostGroup::Ptr hg = HostGroup::GetByName(name);
 
diff --git a/lib/icinga/service.cpp b/lib/icinga/service.cpp
index 61a65b55e..5a526d55e 100644
--- a/lib/icinga/service.cpp
+++ b/lib/icinga/service.cpp
@@ -58,6 +58,8 @@ void Service::OnConfigLoaded(void)
 	Array::Ptr groups = GetGroups();
 
 	if (groups) {
+		ObjectLock olock(groups);
+
 		BOOST_FOREACH(const String& name, groups) {
 			ServiceGroup::Ptr sg = ServiceGroup::GetByName(name);
 
diff --git a/lib/icinga/user.cpp b/lib/icinga/user.cpp
index 2cda97928..9245c8283 100644
--- a/lib/icinga/user.cpp
+++ b/lib/icinga/user.cpp
@@ -21,6 +21,7 @@
 #include "icinga/usergroup.h"
 #include "base/dynamictype.h"
 #include "base/utility.h"
+#include "base/objectlock.h"
 #include <boost/smart_ptr/make_shared.hpp>
 
 using namespace icinga;
@@ -32,6 +33,8 @@ void User::OnConfigLoaded(void)
 	Array::Ptr groups = GetGroups();
 
 	if (groups) {
+		ObjectLock olock(groups);
+
 		BOOST_FOREACH(const String& name, groups) {
 			UserGroup::Ptr ug = UserGroup::GetByName(name);
 
@@ -48,6 +51,8 @@ void User::Stop(void)
 	Array::Ptr groups = GetGroups();
 
 	if (groups) {
+		ObjectLock olock(groups);
+
 		BOOST_FOREACH(const String& name, groups) {
 			UserGroup::Ptr ug = UserGroup::GetByName(name);