diff --git a/libs/ardour/audiosource.cc b/libs/ardour/audiosource.cc
index 3d6e804a60..36a667d109 100644
--- a/libs/ardour/audiosource.cc
+++ b/libs/ardour/audiosource.cc
@@ -374,7 +374,7 @@ AudioSource::read_peaks_with_fpp (PeakData *peaks, nframes_t npeaks, nframes_t s
 		}
 
 		if (zero_fill) {
-			memset (peaks + npeaks - zero_fill, 0, sizeof (PeakData) * zero_fill);
+			memset (&peaks[npeaks], 0, sizeof (PeakData) * zero_fill);
 		}
 
 		return 0;
@@ -485,7 +485,7 @@ AudioSource::read_peaks_with_fpp (PeakData *peaks, nframes_t npeaks, nframes_t s
 		}
 
 		if (zero_fill) {
- 			memset (peaks + npeaks - zero_fill, 0, sizeof (PeakData) * zero_fill);
+ 			memset (&peaks[npeaks], 0, sizeof (PeakData) * zero_fill);
  		}
 		
 		ret = 0;
@@ -562,7 +562,7 @@ AudioSource::read_peaks_with_fpp (PeakData *peaks, nframes_t npeaks, nframes_t s
 		}
 		
 		if (zero_fill) {
-			memset (peaks + npeaks - zero_fill, 0, sizeof (PeakData) * zero_fill);
+			memset (&peaks[npeaks], 0, sizeof (PeakData) * zero_fill);
 		}
 
 		ret = 0;