diff --git a/lib/icinga/icinga-type.conf b/lib/icinga/icinga-type.conf
index f32d378b5..049eadc1d 100644
--- a/lib/icinga/icinga-type.conf
+++ b/lib/icinga/icinga-type.conf
@@ -246,6 +246,8 @@
 }
 
 %type ScheduledDowntime %inherits CustomVarObject {
+	%validator "ValidateScheduledDowntimeRanges",
+
 	%require "host_name",
 	%attribute %name(Host) "host_name",
 	%attribute %string "service_name",
diff --git a/lib/icinga/scheduleddowntime.cpp b/lib/icinga/scheduleddowntime.cpp
index 7ce5e7c19..446e25281 100644
--- a/lib/icinga/scheduleddowntime.cpp
+++ b/lib/icinga/scheduleddowntime.cpp
@@ -34,6 +34,7 @@
 using namespace icinga;
 
 REGISTER_TYPE(ScheduledDowntime);
+REGISTER_SCRIPTFUNCTION(ValidateScheduledDowntimeRanges, &ScheduledDowntime::ValidateRanges);
 
 INITIALIZE_ONCE(&ScheduledDowntime::StaticInitialize);
 
@@ -179,3 +180,35 @@ void ScheduledDowntime::CreateNextDowntime(void)
 	Downtime::Ptr downtime = Checkable::GetDowntimeByID(uid);
 	downtime->SetConfigOwner(GetName());
 }
+
+void ScheduledDowntime::ValidateRanges(const String& location, const ScheduledDowntime::Ptr& object)
+{
+	Dictionary::Ptr ranges = object->GetRanges();
+
+	if (!ranges)
+		return;
+
+	/* create a fake time environment to validate the definitions */
+	time_t refts = Utility::GetTime();
+	tm reference = Utility::LocalTime(refts);
+	Array::Ptr segments = new Array();
+
+	ObjectLock olock(ranges);
+	BOOST_FOREACH(const Dictionary::Pair& kv, ranges) {
+		try {
+			tm begin_tm, end_tm;
+			int stride;
+			LegacyTimePeriod::ParseTimeRange(kv.first, &begin_tm, &end_tm, &stride, &reference);
+		} catch (std::exception&) {
+			BOOST_THROW_EXCEPTION(ScriptError("Validation failed for " +
+			    location + ": Invalid time specification.", object->GetDebugInfo()));
+		}
+
+		try {
+			LegacyTimePeriod::ProcessTimeRanges(kv.second, &reference, segments);
+		} catch (std::exception&) {
+			BOOST_THROW_EXCEPTION(ScriptError("Validation failed for " +
+			    location + ": Invalid time range definition.", object->GetDebugInfo()));
+		}
+	}
+}
diff --git a/lib/icinga/scheduleddowntime.hpp b/lib/icinga/scheduleddowntime.hpp
index 22394c5a4..a4f5273d3 100644
--- a/lib/icinga/scheduleddowntime.hpp
+++ b/lib/icinga/scheduleddowntime.hpp
@@ -53,6 +53,8 @@ public:
 	static void EvaluateApplyRules(const intrusive_ptr<Host>& host);
 	static void EvaluateApplyRules(const intrusive_ptr<Service>& service);
 
+	static void ValidateRanges(const String& location, const ScheduledDowntime::Ptr& object);
+
 protected:
 	virtual void OnAllConfigLoaded(void);
 	virtual void Start(void);