diff --git a/extras/JuceDemo/Source/demos/AudioDemoPlaybackPage.cpp b/extras/JuceDemo/Source/demos/AudioDemoPlaybackPage.cpp
index b9a6fbcf2d..59d0bbacd6 100644
--- a/extras/JuceDemo/Source/demos/AudioDemoPlaybackPage.cpp
+++ b/extras/JuceDemo/Source/demos/AudioDemoPlaybackPage.cpp
@@ -186,8 +186,8 @@ AudioDemoPlaybackPage::AudioDemoPlaybackPage (AudioDeviceManager& deviceManager_
 AudioDemoPlaybackPage::~AudioDemoPlaybackPage()
 {
     //[Destructor_pre]. You can add your own custom destruction code here..
-    transportSource.setSource (0);
-    audioSourcePlayer.setSource (0);
+    transportSource.setSource (nullptr);
+    audioSourcePlayer.setSource (nullptr);
 
     deviceManager.removeAudioCallback (&audioSourcePlayer);
     fileTreeComp->removeListener (this);
@@ -285,8 +285,8 @@ void AudioDemoPlaybackPage::loadFileIntoTransport (const File& audioFile)
 {
     // unload the previous file source and delete it..
     transportSource.stop();
-    transportSource.setSource (0);
-    currentAudioFileSource = 0;
+    transportSource.setSource (nullptr);
+    currentAudioFileSource = nullptr;
 
     // get a format manager and set it up with the basic types (wav and aiff).
     AudioFormatManager formatManager;
@@ -294,7 +294,7 @@ void AudioDemoPlaybackPage::loadFileIntoTransport (const File& audioFile)
 
     AudioFormatReader* reader = formatManager.createReaderFor (audioFile);
 
-    if (reader != 0)
+    if (reader != nullptr)
     {
         currentAudioFileSource = new AudioFormatReaderSource (reader, true);
 
diff --git a/modules/juce_audio_basics/buffers/juce_AudioSampleBuffer.cpp b/modules/juce_audio_basics/buffers/juce_AudioSampleBuffer.cpp
index 4469a36138..5c3a95610e 100644
--- a/modules/juce_audio_basics/buffers/juce_AudioSampleBuffer.cpp
+++ b/modules/juce_audio_basics/buffers/juce_AudioSampleBuffer.cpp
@@ -153,6 +153,7 @@ void AudioSampleBuffer::setSize (const int newNumChannels,
                                  const bool avoidReallocating) noexcept
 {
     jassert (newNumChannels > 0);
+    jassert (newNumSamples >= 0);
 
     if (newNumSamples != size || newNumChannels != numChannels)
     {
diff --git a/modules/juce_audio_basics/sources/juce_BufferingAudioSource.cpp b/modules/juce_audio_basics/sources/juce_BufferingAudioSource.cpp
index 9dd68bd522..19d840b45e 100644
--- a/modules/juce_audio_basics/sources/juce_BufferingAudioSource.cpp
+++ b/modules/juce_audio_basics/sources/juce_BufferingAudioSource.cpp
@@ -39,7 +39,8 @@ BufferingAudioSource::BufferingAudioSource (PositionableAudioSource* source_,
       bufferValidStart (0),
       bufferValidEnd (0),
       nextPlayPos (0),
-      wasSourceLooping (false)
+      wasSourceLooping (false),
+      isPrepared (false)
 {
     jassert (source_ != nullptr);
 
@@ -55,28 +56,39 @@ BufferingAudioSource::~BufferingAudioSource()
 //==============================================================================
 void BufferingAudioSource::prepareToPlay (int samplesPerBlockExpected, double sampleRate_)
 {
-    source->prepareToPlay (samplesPerBlockExpected, sampleRate_);
+    const int bufferSizeNeeded = jmax (samplesPerBlockExpected * 2, numberOfSamplesToBuffer);
 
-    sampleRate = sampleRate_;
+    if (sampleRate_ != sampleRate
+         || bufferSizeNeeded != buffer.getNumSamples()
+         || ! isPrepared)
+    {
+        backgroundThread.removeTimeSliceClient (this);
 
-    buffer.setSize (numberOfChannels, jmax (samplesPerBlockExpected * 2, numberOfSamplesToBuffer));
-    buffer.clear();
+        isPrepared = true;
+        sampleRate = sampleRate_;
 
-    bufferValidStart = 0;
-    bufferValidEnd = 0;
+        source->prepareToPlay (samplesPerBlockExpected, sampleRate_);
 
-    backgroundThread.addTimeSliceClient (this);
+        buffer.setSize (numberOfChannels, bufferSizeNeeded);
+        buffer.clear();
+
+        bufferValidStart = 0;
+        bufferValidEnd = 0;
 
-    while (bufferValidEnd - bufferValidStart < jmin (((int) sampleRate_) / 4,
-                                                     buffer.getNumSamples() / 2))
-    {
         backgroundThread.addTimeSliceClient (this);
-        Thread::sleep (5);
+
+        while (bufferValidEnd - bufferValidStart < jmin (((int) sampleRate_) / 4,
+                                                         buffer.getNumSamples() / 2))
+        {
+            backgroundThread.addTimeSliceClient (this);
+            Thread::sleep (5);
+        }
     }
 }
 
 void BufferingAudioSource::releaseResources()
 {
+    isPrepared = false;
     backgroundThread.removeTimeSliceClient (this);
 
     buffer.setSize (numberOfChannels, 0);
@@ -108,8 +120,9 @@ void BufferingAudioSource::getNextAudioBlock (const AudioSourceChannelInfo& info
         {
             for (int chan = jmin (numberOfChannels, info.buffer->getNumChannels()); --chan >= 0;)
             {
+                jassert (buffer.getNumSamples() > 0);
                 const int startBufferIndex = (int) ((validStart + nextPlayPos) % buffer.getNumSamples());
-                const int endBufferIndex = (int) ((validEnd + nextPlayPos) % buffer.getNumSamples());
+                const int endBufferIndex   = (int) ((validEnd + nextPlayPos)   % buffer.getNumSamples());
 
                 if (startBufferIndex < endBufferIndex)
                 {
@@ -144,6 +157,7 @@ void BufferingAudioSource::getNextAudioBlock (const AudioSourceChannelInfo& info
 
 int64 BufferingAudioSource::getNextReadPosition() const
 {
+    jassert (source->getTotalLength() > 0);
     return (source->isLooping() && nextPlayPos > 0)
                     ? nextPlayPos % source->getTotalLength()
                     : nextPlayPos;
@@ -204,8 +218,9 @@ bool BufferingAudioSource::readNextBufferChunk()
 
     if (sectionToReadStart != sectionToReadEnd)
     {
+        jassert (buffer.getNumSamples() > 0);
         const int bufferIndexStart = (int) (sectionToReadStart % buffer.getNumSamples());
-        const int bufferIndexEnd = (int) (sectionToReadEnd % buffer.getNumSamples());
+        const int bufferIndexEnd   = (int) (sectionToReadEnd   % buffer.getNumSamples());
 
         if (bufferIndexStart < bufferIndexEnd)
         {
diff --git a/modules/juce_audio_basics/sources/juce_BufferingAudioSource.h b/modules/juce_audio_basics/sources/juce_BufferingAudioSource.h
index b8d00cb18e..834cb0dd91 100644
--- a/modules/juce_audio_basics/sources/juce_BufferingAudioSource.h
+++ b/modules/juce_audio_basics/sources/juce_BufferingAudioSource.h
@@ -101,7 +101,7 @@ private:
     CriticalSection bufferStartPosLock;
     int64 volatile bufferValidStart, bufferValidEnd, nextPlayPos;
     double volatile sampleRate;
-    bool wasSourceLooping;
+    bool wasSourceLooping, isPrepared;
 
     friend class SharedBufferingAudioSourceThread;
     bool readNextBufferChunk();
diff --git a/modules/juce_audio_devices/sources/juce_AudioTransportSource.cpp b/modules/juce_audio_devices/sources/juce_AudioTransportSource.cpp
index 6df7a02c63..da9cf78356 100644
--- a/modules/juce_audio_devices/sources/juce_AudioTransportSource.cpp
+++ b/modules/juce_audio_devices/sources/juce_AudioTransportSource.cpp
@@ -63,7 +63,7 @@ void AudioTransportSource::setSource (PositionableAudioSource* const newSource,
         if (source == nullptr)
             return;
 
-        setSource (0, 0, 0); // deselect and reselect to avoid releasing resources wrongly
+        setSource (nullptr, 0, nullptr); // deselect and reselect to avoid releasing resources wrongly
     }
 
     readAheadBufferSize = readAheadBufferSize_;
diff --git a/modules/juce_audio_formats/codecs/juce_CoreAudioFormat.cpp b/modules/juce_audio_formats/codecs/juce_CoreAudioFormat.cpp
index a01ad43e8c..6f389f61e8 100644
--- a/modules/juce_audio_formats/codecs/juce_CoreAudioFormat.cpp
+++ b/modules/juce_audio_formats/codecs/juce_CoreAudioFormat.cpp
@@ -54,7 +54,6 @@ namespace
 class CoreAudioReader : public AudioFormatReader
 {
 public:
-    //==============================================================================
     CoreAudioReader (InputStream* const inp)
         : AudioFormatReader (inp, TRANS (coreAudioFormatName)),
           ok (false), lastReadPosition (0)