diff --git a/lib/checker/checkercomponent.cpp b/lib/checker/checkercomponent.cpp
index c26db9de1..89426f8a1 100644
--- a/lib/checker/checkercomponent.cpp
+++ b/lib/checker/checkercomponent.cpp
@@ -174,6 +174,9 @@ void CheckerComponent::CheckThreadProc()
 			m_IdleCheckables.insert(GetCheckableScheduleInfo(checkable));
 			lock.unlock();
 
+			Log(LogDebug, "CheckerComponent")
+				<< "Checks for checkable '" << checkable->GetName() << "' are disabled. Rescheduling check.";
+
 			checkable->UpdateNextCheck();
 
 			lock.lock();
@@ -181,7 +184,16 @@ void CheckerComponent::CheckThreadProc()
 			continue;
 		}
 
-		m_PendingCheckables.insert(GetCheckableScheduleInfo(checkable));
+
+		csi = GetCheckableScheduleInfo(checkable);
+
+		Log(LogDebug, "CheckerComponent")
+			<< "Scheduling info for checkable '" << checkable->GetName() << "' ("
+			<< Utility::FormatDateTime("%Y-%m-%d %H:%M:%S %z", checkable->GetNextCheck()) << "): Object '"
+			<< csi.Object->GetName() << "', Next Check: "
+			<< Utility::FormatDateTime("%Y-%m-%d %H:%M:%S %z", csi.NextCheck) << "(" << csi.NextCheck << ").";
+
+		m_PendingCheckables.insert(csi);
 
 		lock.unlock();
 
diff --git a/lib/icinga/checkable-check.cpp b/lib/icinga/checkable-check.cpp
index 719611aba..faf50694a 100644
--- a/lib/icinga/checkable-check.cpp
+++ b/lib/icinga/checkable-check.cpp
@@ -81,7 +81,14 @@ void Checkable::UpdateNextCheck(const MessageOrigin::Ptr& origin)
 
 	adj = std::min(0.5 + fmod(GetSchedulingOffset(), interval * 5) / 100.0, adj);
 
-	SetNextCheck(now - adj + interval, false, origin);
+	double nextCheck = now - adj + interval;
+
+	Log(LogDebug, "Checkable")
+		<< "Update checkable '" << GetName() << "' with check interval '" << GetCheckInterval()
+		<< "' from last check time at " << Utility::FormatDateTime("%Y-%m-%d %H:%M:%S %z", GetLastCheck())
+		<< " (" << GetLastCheck() << ") to next check time at " << Utility::FormatDateTime("%Y-%m-%d %H:%M:%S %z", nextCheck) << "(" << nextCheck << ").";
+
+	SetNextCheck(nextCheck, false, origin);
 }
 
 bool Checkable::HasBeenChecked() const
@@ -431,6 +438,12 @@ void Checkable::ExecuteCheck()
 	double scheduled_start = GetNextCheck();
 	double before_check = Utility::GetTime();
 
+	/* This calls SetNextCheck() which updates the CheckerComponent's idle/pending
+	 * queues and ensures that checks are not fired multiple times. ProcessCheckResult()
+	 * is called too late. See #6421.
+	 */
+	UpdateNextCheck();
+
 	bool reachable = IsReachable();
 
 	{