diff --git a/oscar/SleepLib/day.cpp b/oscar/SleepLib/day.cpp
index 7f290d85..b2dda6be 100644
--- a/oscar/SleepLib/day.cpp
+++ b/oscar/SleepLib/day.cpp
@@ -1,5 +1,6 @@
 /* SleepLib Day Class Implementation
  *
+ * Copyright (c) 2019 The OSCAR Team
  * Copyright (c) 2011-2018 Mark Watkins <mark@jedimark.net>
  *
  * This file is subject to the terms and conditions of the GNU General Public
@@ -1341,6 +1342,35 @@ bool Day::hasMachine(Machine * mach)
     return false;
 }
 
+void Day::removeMachine(Machine * mach)
+{
+    // Yell about and fix any dangling references rather than possibly crashing later.
+    //
+    // This has no functional use and can be removed when the data structures are cleaned up
+    // with better encapsulation and fewer unnecessary references between each other.
+    
+    QList<Session*> list = sessions;  // make a copy so the iterator doesn't get broken by removals
+    for (auto & sess : list) {
+        if (sess->machine() == mach) {
+            // This indicates a problem with the Machine class not tracking all of its sessions, for
+            // example if there's a duplicate session ID.
+            qCritical() << "Day object" << this->date().toString()
+                        << "session" << sess->session() << "refers to machine" << mach->serial();
+            removeSession(sess);
+        }
+    }
+    
+    for (auto & m : machines.keys()) {
+        if (machines[m] == mach) {
+            // This indicates a problem internal to the Day class, since removeSession should remove
+            // machines from this list if there are no longer any sessions pointing to it.
+            qCritical() << "Day object" << this->date().toString()
+                        << "refers to machine" << mach->serial();
+            machines.remove(m);
+        }
+    }
+}
+
 QString Day::getCPAPMode()
 {
     Machine * mach = machine(MT_CPAP);
diff --git a/oscar/SleepLib/day.h b/oscar/SleepLib/day.h
index bb74e48c..0415d8c3 100644
--- a/oscar/SleepLib/day.h
+++ b/oscar/SleepLib/day.h
@@ -1,5 +1,6 @@
-/* SleepLib Day Class Header
+/* SleepLib Day Class Header
  *
+ * Copyright (c) 2019 The OSCAR Team
  * Copyright (C) 2011-2018 Mark Watkins <mark@jedimark.net>
  *
  * This file is subject to the terms and conditions of the GNU General Public
@@ -100,6 +101,9 @@ class Day
     //! \brief Returns true if any sessions have records matching specific machine type
     bool searchMachine(MachineType mt);
 
+    //! \brief Removes any lingering references to a specific machine record and emits a warning if there were any
+    void removeMachine(Machine * mach);
+
     //! \brief Returns the Average of all Sessions setting 'code' for this day
     EventDataType settings_avg(ChannelID code);
 
diff --git a/oscar/SleepLib/machine.cpp b/oscar/SleepLib/machine.cpp
index 17a166cd..cf209ba1 100644
--- a/oscar/SleepLib/machine.cpp
+++ b/oscar/SleepLib/machine.cpp
@@ -519,6 +519,7 @@ bool Machine::Purge(int secret)
 
     // Create a copy of the list so the hash can be manipulated
     QList<Session *> sessions = sessionlist.values();
+    QList<Day *> days = day.values();
 
     // Clean up any loaded sessions from memory first..
     //bool success = true;
@@ -533,6 +534,10 @@ bool Machine::Purge(int secret)
 
         delete sess;
     }
+    // Make sure there aren't any dangling references to this machine
+    for (auto & d : days) {
+        d->removeMachine(this);
+    }
 
     // Remove EVERYTHING under Events folder..
     QString eventspath = getEventsPath();