diff --git a/src/StretcherChannelData.cpp b/src/StretcherChannelData.cpp
index 2c1225f..5ddc30f 100644
--- a/src/StretcherChannelData.cpp
+++ b/src/StretcherChannelData.cpp
@@ -86,6 +86,7 @@ RubberBandStretcher::Impl::ChannelData::construct(const std::set<size_t> &sizes,
 
     accumulator = allocate_and_zero<float>(maxSize);
     windowAccumulator = allocate_and_zero<float>(maxSize);
+    ms = allocate_and_zero<float>(maxSize);
     interpolator = allocate_and_zero<float>(maxSize);
     interpolatorScale = 0;
 
@@ -176,8 +177,8 @@ RubberBandStretcher::Impl::ChannelData::setSizes(size_t windowSize,
     envelope = reallocate_and_zero(envelope, oldReal, realSize);
     fltbuf = reallocate_and_zero(fltbuf, oldMax, maxSize);
     dblbuf = reallocate_and_zero(dblbuf, oldMax, maxSize);
-
-    interpolator = reallocate_and_zero<float>(interpolator, oldMax, maxSize);
+    ms = reallocate_and_zero(ms, oldMax, maxSize);
+    interpolator = reallocate_and_zero(interpolator, oldMax, maxSize);
 
     // But we do want to preserve data in these
 
@@ -243,6 +244,8 @@ RubberBandStretcher::Impl::ChannelData::~ChannelData()
     deallocate(prevError);
     deallocate(unwrappedPhase);
     deallocate(envelope);
+    deallocate(interpolator);
+    deallocate(ms);
     deallocate(accumulator);
     deallocate(windowAccumulator);
     deallocate(fltbuf);
diff --git a/src/StretcherChannelData.h b/src/StretcherChannelData.h
index 93b4ce8..05f6cf4 100644
--- a/src/StretcherChannelData.h
+++ b/src/StretcherChannelData.h
@@ -111,6 +111,7 @@ public:
     float *accumulator;
     size_t accumulatorFill;
     float *windowAccumulator;
+    float *ms; // only used when mid-side processing
     float *interpolator; // only used when time-domain smoothing is on
     int interpolatorScale;
 
diff --git a/src/StretcherProcess.cpp b/src/StretcherProcess.cpp
index 05b9ddf..2bf152a 100644
--- a/src/StretcherProcess.cpp
+++ b/src/StretcherProcess.cpp
@@ -183,7 +183,6 @@ RubberBandStretcher::Impl::consumeChannel(size_t c,
 
     bool resampling = resampleBeforeStretching();
 
-    float *ms = 0;
     const float *input = 0;
 
     bool useMidSide = ((m_options & OptionChannelsTogether) &&
@@ -214,9 +213,8 @@ RubberBandStretcher::Impl::consumeChannel(size_t c,
 #endif
 
         if (useMidSide) {
-            ms = (float *)alloca(samples * sizeof(float));
-            prepareChannelMS(c, inputs, offset, samples, ms);
-            input = ms;
+            prepareChannelMS(c, inputs, offset, samples, cd.ms);
+            input = cd.ms;
         } else {
             input = inputs[c] + offset;
         }
@@ -252,9 +250,8 @@ RubberBandStretcher::Impl::consumeChannel(size_t c,
     } else {
 
         if (useMidSide) {
-            ms = (float *)alloca(toWrite * sizeof(float));
-            prepareChannelMS(c, inputs, offset, toWrite, ms);
-            input = ms;
+            prepareChannelMS(c, inputs, offset, toWrite, cd.ms);
+            input = cd.ms;
         } else {
             input = inputs[c] + offset;
         }