diff --git a/src/mad_dynmap.cpp b/src/mad_dynmap.cpp
index 64c1ce45e..6b8e49e19 100644
--- a/src/mad_dynmap.cpp
+++ b/src/mad_dynmap.cpp
@@ -220,7 +220,7 @@ inline void bxbyh (const cflw<M> &m, const V &x, const V &y, T &bx, T &by)
   int k = -1;
   T btx, bty;
 
-  RFOR(i,m.snm) {
+  RFOR(i,m.snm+1, 1) {
     btx = 0., bty = 0.;
 
     RFOR(j,m.snm-i) { ++k;
diff --git a/src/madl_dynmap.mad b/src/madl_dynmap.mad
index b32483724..e7b77d5a3 100644
--- a/src/madl_dynmap.mad
+++ b/src/madl_dynmap.mad
@@ -127,8 +127,8 @@ local function bxbyh (snm, bfx, bfy, x, y)
     bty = (bty + bfy[k]) * y
   end
   
-  bx = bx + btx + bfx[k+1]
-  by = by + bty + bfy[k+1]
+  bx = bx + (btx + bfx[k+1])
+  by = by + (bty + bfy[k+1])
 
   return bx, by
 end