diff --git a/libs/ardour/interpolation.cc b/libs/ardour/interpolation.cc
index 47e3642bf3..1393d8aae8 100644
--- a/libs/ardour/interpolation.cc
+++ b/libs/ardour/interpolation.cc
@@ -117,6 +117,7 @@ CubicInterpolation::interpolate (int channel, nframes_t nframes, Sample *input,
 								fractional_phase_part * (3.0f * (input[i] - input[i+1]) - inm1 + input[i+2])));
 
 		    distance += _speed + acceleration;
+		    inm1 = input[i];
 	    }
 
     } else {