diff --git a/modules/juce_audio_devices/midi_io/juce_MidiMessageCollector.cpp b/modules/juce_audio_devices/midi_io/juce_MidiMessageCollector.cpp
index 50ca20569a..97f7330340 100644
--- a/modules/juce_audio_devices/midi_io/juce_MidiMessageCollector.cpp
+++ b/modules/juce_audio_devices/midi_io/juce_MidiMessageCollector.cpp
@@ -34,9 +34,10 @@ MidiMessageCollector::~MidiMessageCollector()
 //==============================================================================
 void MidiMessageCollector::reset (const double newSampleRate)
 {
+    const ScopedLock sl (midiCallbackLock);
+
     jassert (newSampleRate > 0);
 
-    const ScopedLock sl (midiCallbackLock);
    #if JUCE_DEBUG
     hasCalledReset = true;
    #endif
@@ -47,6 +48,8 @@ void MidiMessageCollector::reset (const double newSampleRate)
 
 void MidiMessageCollector::addMessageToQueue (const MidiMessage& message)
 {
+    const ScopedLock sl (midiCallbackLock);
+
    #if JUCE_DEBUG
     jassert (hasCalledReset); // you need to call reset() to set the correct sample rate before using this object
    #endif
@@ -55,8 +58,6 @@ void MidiMessageCollector::addMessageToQueue (const MidiMessage& message)
     // for details of what the number should be.
     jassert (message.getTimeStamp() != 0);
 
-    const ScopedLock sl (midiCallbackLock);
-
     auto sampleNumber = (int) ((message.getTimeStamp() - 0.001 * lastCallbackTime) * sampleRate);
 
     incomingMessages.addEvent (message, sampleNumber);
@@ -70,6 +71,8 @@ void MidiMessageCollector::addMessageToQueue (const MidiMessage& message)
 void MidiMessageCollector::removeNextBlockOfMessages (MidiBuffer& destBuffer,
                                                       const int numSamples)
 {
+    const ScopedLock sl (midiCallbackLock);
+
    #if JUCE_DEBUG
     jassert (hasCalledReset); // you need to call reset() to set the correct sample rate before using this object
    #endif
@@ -79,7 +82,6 @@ void MidiMessageCollector::removeNextBlockOfMessages (MidiBuffer& destBuffer,
     auto timeNow = Time::getMillisecondCounterHiRes();
     auto msElapsed = timeNow - lastCallbackTime;
 
-    const ScopedLock sl (midiCallbackLock);
     lastCallbackTime = timeNow;
 
     if (! incomingMessages.isEmpty())
diff --git a/modules/juce_audio_processors/format_types/juce_VSTPluginFormat.cpp b/modules/juce_audio_processors/format_types/juce_VSTPluginFormat.cpp
index e8208f2ccf..b6eb6b8596 100644
--- a/modules/juce_audio_processors/format_types/juce_VSTPluginFormat.cpp
+++ b/modules/juce_audio_processors/format_types/juce_VSTPluginFormat.cpp
@@ -2052,7 +2052,8 @@ private:
     //==============================================================================
     String name;
     CriticalSection lock;
-    bool wantsMidiMessages = false, initialised = false, isPowerOn = false;
+    std::atomic<bool> wantsMidiMessages { false };
+    bool initialised = false, isPowerOn = false;
     bool lastProcessBlockCallWasBypass = false, vstSupportsBypass = false;
     mutable StringArray programNames;
     AudioBuffer<float> outOfPlaceBuffer;
diff --git a/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.cpp b/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.cpp
index 123b2e396e..37014a9295 100644
--- a/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.cpp
+++ b/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.cpp
@@ -806,6 +806,8 @@ AudioProcessorGraph::Node::Node (NodeID n, std::unique_ptr<AudioProcessor> p) no
 void AudioProcessorGraph::Node::prepare (double newSampleRate, int newBlockSize,
                                          AudioProcessorGraph* graph, ProcessingPrecision precision)
 {
+    const ScopedLock lock (processorLock);
+
     if (! isPrepared)
     {
         isPrepared = true;
@@ -822,6 +824,8 @@ void AudioProcessorGraph::Node::prepare (double newSampleRate, int newBlockSize,
 
 void AudioProcessorGraph::Node::unprepare()
 {
+    const ScopedLock lock (processorLock);
+
     if (isPrepared)
     {
         isPrepared = false;
@@ -831,6 +835,8 @@ void AudioProcessorGraph::Node::unprepare()
 
 void AudioProcessorGraph::Node::setParentGraph (AudioProcessorGraph* const graph) const
 {
+    const ScopedLock lock (processorLock);
+
     if (auto* ioProc = dynamic_cast<AudioProcessorGraph::AudioGraphIOProcessor*> (processor.get()))
         ioProc->setParentGraph (graph);
 }
@@ -940,7 +946,12 @@ AudioProcessorGraph::Node::Ptr AudioProcessorGraph::addNode (std::unique_ptr<Aud
     newProcessor->setPlayHead (getPlayHead());
 
     Node::Ptr n (new Node (nodeID, std::move (newProcessor)));
-    nodes.add (n.get());
+
+    {
+        const ScopedLock sl (getCallbackLock());
+        nodes.add (n.get());
+    }
+
     n->setParentGraph (this);
     topologyChanged();
     return n;
@@ -1233,7 +1244,7 @@ void AudioProcessorGraph::buildRenderingSequence()
 
     const ScopedLock sl (getCallbackLock());
 
-    std::swap (renderSequenceFloat, newSequenceF);
+    std::swap (renderSequenceFloat,  newSequenceF);
     std::swap (renderSequenceDouble, newSequenceD);
 }
 
diff --git a/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.h b/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.h
index f7ce5789fb..c8a1a0b5c5 100644
--- a/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.h
+++ b/modules/juce_audio_processors/processors/juce_AudioProcessorGraph.h
@@ -143,7 +143,8 @@ public:
 
         const std::unique_ptr<AudioProcessor> processor;
         Array<Connection> inputs, outputs;
-        bool isPrepared = false, bypassed = false;
+        bool isPrepared = false;
+        std::atomic<bool> bypassed { false };
 
         Node (NodeID, std::unique_ptr<AudioProcessor>) noexcept;
 
@@ -151,6 +152,8 @@ public:
         void prepare (double newSampleRate, int newBlockSize, AudioProcessorGraph*, ProcessingPrecision);
         void unprepare();
 
+        CriticalSection processorLock;
+
         JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (Node)
     };