--- a/blockproc/blockframeaccel.m
+++ b/blockproc/blockframeaccel.m
@@ -65,8 +65,8 @@
    
    % This is important otherwise we would get 0 coefficients for some
    % blocks.
-   assert(max(Fo.a(:,1)) <= Lb ,['%s: Time step %i is bigger than the',...
-      ' block length %i.'],upper(mfilename),Fo.a,Lb);
+   assert(max(Fo.a(:,1)) <= Lb ,sprintf(['%s: Time step %i is bigger than the',...
+      ' block length %i.'],upper(mfilename),Fo.a,Lb));
    
    Fo.winLen = winLen;