diff --git a/mc_pd_eval3.m b/mc_pd_eval3.m
index 4774df9..1803126 100644
--- a/mc_pd_eval3.m
+++ b/mc_pd_eval3.m
@@ -80,20 +80,25 @@ for n=1:N,
 	_omega(n) = omega;
 end
 
+function y = jmod(x)
+	y = x - fix(x);
+	y = y + 0^(0.5 + sign(y)/2);
+endfunction
+
 function perr = phase_det(lo, x)
-	lo = mod(lo - 0.5, 1);
-	perr = mod((lo - x), 1) - 0.5;
+	lo = jmod(lo - 0.5);
+	perr = jmod(lo - x) - 0.5;
 endfunction
 
 function phase_out = process_linear_phase(phase_in, omega)
-	phase_out = mod(phase + omega, 1);
+	phase_out = jmod(phase + omega);
 endfunction
 
 function [phase_out, y] = process_trigon(y, omega)
 	b = 2.0 * sin(pi*omega);
 	y(1) = y(1) - b*y(2);
 	y(2) = y(2) + b*y(1);
-	phase_out = mod(0.5 + 0.5*atan2(y(1), -y(2))/pi, 1);
+	phase_out = jmod(0.5 + 0.5*atan2(y(1), -y(2))/pi);
 endfunction
 
 close all;