diff --git a/lib/icinga/checkable.hpp b/lib/icinga/checkable.hpp
index 18c1509a9..7a0623ac4 100644
--- a/lib/icinga/checkable.hpp
+++ b/lib/icinga/checkable.hpp
@@ -97,7 +97,7 @@ public:
 	void UpdateNextCheck(const MessageOrigin::Ptr& origin = nullptr);
 
 	bool HasBeenChecked() const;
-	virtual bool IsStateOK(ServiceState state) = 0;
+	virtual bool IsStateOK(ServiceState state) const = 0;
 
 	double GetLastCheck() const final;
 
diff --git a/lib/icinga/host.cpp b/lib/icinga/host.cpp
index 4b95ffa9f..9744eed46 100644
--- a/lib/icinga/host.cpp
+++ b/lib/icinga/host.cpp
@@ -192,7 +192,7 @@ int Host::GetSeverity() const
 	return severity;
 }
 
-bool Host::IsStateOK(ServiceState state)
+bool Host::IsStateOK(ServiceState state) const
 {
 	return Host::CalculateState(state) == HostUp;
 }
diff --git a/lib/icinga/host.hpp b/lib/icinga/host.hpp
index a72a7874c..237d8aaa1 100644
--- a/lib/icinga/host.hpp
+++ b/lib/icinga/host.hpp
@@ -39,7 +39,7 @@ public:
 	HostState GetLastHardState() const override;
 	int GetSeverity() const override;
 
-	bool IsStateOK(ServiceState state) override;
+	bool IsStateOK(ServiceState state) const override;
 	void SaveLastState(ServiceState state, double timestamp) override;
 
 	static HostState StateFromString(const String& state);
diff --git a/lib/icinga/service.cpp b/lib/icinga/service.cpp
index 63fd70445..0b52298f5 100644
--- a/lib/icinga/service.cpp
+++ b/lib/icinga/service.cpp
@@ -133,7 +133,7 @@ int Service::GetSeverity() const
 	return severity;
 }
 
-bool Service::IsStateOK(ServiceState state)
+bool Service::IsStateOK(ServiceState state) const
 {
 	return state == ServiceOK;
 }
diff --git a/lib/icinga/service.hpp b/lib/icinga/service.hpp
index 8617eee3b..8453e8506 100644
--- a/lib/icinga/service.hpp
+++ b/lib/icinga/service.hpp
@@ -32,7 +32,7 @@ public:
 
 	bool ResolveMacro(const String& macro, const CheckResult::Ptr& cr, Value *result) const override;
 
-	bool IsStateOK(ServiceState state) override;
+	bool IsStateOK(ServiceState state) const override;
 	void SaveLastState(ServiceState state, double timestamp) override;
 
 	static ServiceState StateFromString(const String& state);