diff --git a/miscmaths.cc b/miscmaths.cc
index a21f879e909892f8c773c67752b18bf6293b1070..6e42bd39774038a9ddefc25eee381b5e6df229ca 100644
--- a/miscmaths.cc
+++ b/miscmaths.cc
@@ -1046,6 +1046,14 @@ void cart2sph(const ColumnVector& dir, float& th, float& ph)
 
 void cart2sph(const Matrix& dir,ColumnVector& th,ColumnVector& ph)
 {
+  if(th.Nrows()!=dir.Ncols()){
+    th.ReSize(dir.Ncols());
+  }
+
+  if(ph.Nrows()!=dir.Ncols()){
+    ph.ReSize(dir.Ncols());
+  }
+
   for (int i=1;i<=dir.Ncols();i++) {
     float mag=sqrt(dir(1,i)*dir(1,i)+dir(2,i)*dir(2,i)+dir(3,i)*dir(3,i));
     if(mag==0){