diff --git a/sndlock.cpp b/sndlock.cpp
index bc6fddf..a41c7bd 100644
--- a/sndlock.cpp
+++ b/sndlock.cpp
@@ -100,7 +100,7 @@ static void dsp_thread()
             size_t read = sio_read(hdl, buf_in, sizeof(buf_in));
             float scale = powf(0.5f, SND_BITS-1);
             for(int i=0;i<SND_PCHAN;i++)
-                for(int j=0;j<read;j++) {
+                for(int j=0;j<read/sizeof(buf_in[0]);j++) {
                     std::complex<float> rotated;
                     rotated = (float)buf_in[j]*std::polar(scale, phase_in[i]*2.0f*(float)M_PI/(float)UINT32_MAX);
                     phase_in[i] += ftw[i];  // wraps on underflow