diff --git a/miscmaths.cc b/miscmaths.cc
index 9dcff34b0db5ff664fddf7a332efb6ea0b30df26..b02f01817933ef2d54676f0bac83dd0d0bd9ad59 100644
--- a/miscmaths.cc
+++ b/miscmaths.cc
@@ -1032,7 +1032,7 @@ float rms_deviation(const Matrix& affmat1, const Matrix& affmat2,
 
 Matrix mat44_to_newmat(mat44 inmat)
 {
-  Matrix retmat;
+  Matrix retmat(4,4);
   for (int ii=0; ii<4; ii++) {
     for (int jj=0; jj<4; jj++) {
       retmat(ii+1,jj+1) = inmat.m[ii][jj];