diff --git a/src/AudioIO.cpp b/src/AudioIO.cpp
index c403bd49d..4c498a474 100644
--- a/src/AudioIO.cpp
+++ b/src/AudioIO.cpp
@@ -4495,14 +4495,14 @@ int audacityAudioCallback(const void *inputBuffer, void *outputBuffer,
                   // Output volume emulation: possibly copy meter samples, then
                   // apply volume, then copy to the output buffer
                   if (outputMeterFloats != outputFloats)
-                     for (int i = 0; i < len; ++i)
+                     for (decltype(len) i = 0; i < len; ++i)
                         outputMeterFloats[numPlaybackChannels*i] +=
                            gain*tempFloats[i];
 
                   if (gAudioIO->mEmulateMixerOutputVol)
                      gain *= gAudioIO->mMixerOutputVol;
 
-                  for(int i=0; i<len; i++)
+                  for(decltype(len) i = 0; i < len; i++)
                      outputFloats[numPlaybackChannels*i] += gain*tempBufs[c][i];
                }
 
@@ -4513,14 +4513,14 @@ int audacityAudioCallback(const void *inputBuffer, void *outputBuffer,
 
                   // Output volume emulation (as above)
                   if (outputMeterFloats != outputFloats)
-                     for (int i = 0; i < len; ++i)
+                     for (decltype(len) i = 0; i < len; ++i)
                         outputMeterFloats[numPlaybackChannels*i+1] +=
                            gain*tempFloats[i];
 
                   if (gAudioIO->mEmulateMixerOutputVol)
                      gain *= gAudioIO->mMixerOutputVol;
 
-                  for(int i=0; i<len; i++)
+                  for(decltype(len) i = 0; i < len; i++)
                      outputFloats[numPlaybackChannels*i+1] += gain*tempBufs[c][i];
                }
             }
diff --git a/src/BlockFile.cpp b/src/BlockFile.cpp
index 56c0e5e56..6098003eb 100644
--- a/src/BlockFile.cpp
+++ b/src/BlockFile.cpp
@@ -387,7 +387,7 @@ void BlockFile::GetMinMax(sampleCount start, sampleCount len,
    float max = -FLT_MAX;
    float sumsq = 0;
 
-   for( int i = 0; i < len; i++ )
+   for( decltype(len) i = 0; i < len; i++ )
    {
       float sample = ((float*)blockData.ptr())[i];
 
@@ -447,8 +447,7 @@ bool BlockFile::Read256(float *buffer,
 
    if (mSummaryInfo.fields == 2) {
       // No RMS info
-      int i;
-      for(i=len-1; i>=0; i--) {
+      for(auto i = len; i--;) {
          buffer[3*i+2] = (fabs(buffer[2*i]) + fabs(buffer[2*i+1]))/4.0;
          buffer[3*i+1] = buffer[2*i+1];
          buffer[3*i] = buffer[2*i];
@@ -488,8 +487,7 @@ bool BlockFile::Read64K(float *buffer,
 
    if (mSummaryInfo.fields == 2) {
       // No RMS info; make guess
-      int i;
-      for(i=len-1; i>=0; i--) {
+      for(auto i = len; i--;) {
          buffer[3*i+2] = (fabs(buffer[2*i]) + fabs(buffer[2*i+1]))/4.0;
          buffer[3*i+1] = buffer[2*i+1];
          buffer[3*i] = buffer[2*i];
diff --git a/src/Mix.cpp b/src/Mix.cpp
index c0e171939..6f92d55b2 100644
--- a/src/Mix.cpp
+++ b/src/Mix.cpp
@@ -573,7 +573,7 @@ sampleCount Mixer::MixSameRate(int *channelFlags, WaveTrackCache &cache,
       auto results = cache.Get(floatSample, *pos - (slen - 1), slen);
       memcpy(mFloatBuffer, results, sizeof(float) * slen);
       track->GetEnvelopeValues(mEnvValues, slen, t - (slen - 1) / mRate);
-      for(int i=0; i<slen; i++)
+      for(decltype(slen) i = 0; i < slen; i++)
          mFloatBuffer[i] *= mEnvValues[i]; // Track gain control will go here?
       ReverseSamples((samplePtr)mFloatBuffer, floatSample, 0, slen);
 
@@ -583,7 +583,7 @@ sampleCount Mixer::MixSameRate(int *channelFlags, WaveTrackCache &cache,
       auto results = cache.Get(floatSample, *pos, slen);
       memcpy(mFloatBuffer, results, sizeof(float) * slen);
       track->GetEnvelopeValues(mEnvValues, slen, t);
-      for(int i=0; i<slen; i++)
+      for(decltype(slen) i = 0; i < slen; i++)
          mFloatBuffer[i] *= mEnvValues[i]; // Track gain control will go here?
 
       *pos += slen;
diff --git a/src/Sequence.cpp b/src/Sequence.cpp
index 19fd89497..34749a6f8 100644
--- a/src/Sequence.cpp
+++ b/src/Sequence.cpp
@@ -1764,7 +1764,7 @@ bool Sequence::ConsistencyCheck(const wxChar *whereStr) const
 void Sequence::DebugPrintf(wxString *dest) const
 {
    unsigned int i;
-   int pos = 0;
+   decltype(mNumSamples) pos = 0;
 
    for (i = 0; i < mBlock.size(); i++) {
       const SeqBlock &seqBlock = mBlock[i];
diff --git a/src/blockfile/SimpleBlockFile.cpp b/src/blockfile/SimpleBlockFile.cpp
index 022768560..fcfb8be56 100644
--- a/src/blockfile/SimpleBlockFile.cpp
+++ b/src/blockfile/SimpleBlockFile.cpp
@@ -624,10 +624,11 @@ void SimpleBlockFile::Recover(){
    header.channels = 1;
    file.Write(&header, sizeof(header));
 
-   for(i=0;i<mSummaryInfo.totalSummaryBytes;i++)
+   for(decltype(mSummaryInfo.totalSummaryBytes) i = 0;
+       i < mSummaryInfo.totalSummaryBytes; i++)
       file.Write(wxT("\0"),1);
 
-   for(i=0;i<mLen*2;i++)
+   for(decltype(mLen) i = 0; i < mLen * 2; i++)
       file.Write(wxT("\0"),1);
 
 }