diff --git a/horace_core/utilities/@MagneticIons/getFF_calculator.m b/horace_core/utilities/@MagneticIons/getFF_calculator.m
index 04419efac6..32db718357 100644
--- a/horace_core/utilities/@MagneticIons/getFF_calculator.m
+++ b/horace_core/utilities/@MagneticIons/getFF_calculator.m
@@ -44,14 +44,25 @@
 %
 
 if isa(win,'sqw')
-    self.hkl_to_Qmat_ = win.data.proj.bmatrix();
+    self.proj_ = win.data.proj;
 elseif isnumeric(win) || all(size(win) == [3,3])
-    self.hkl_to_Qmat_= win;
+    proj = line_proj([1,0,0], [0,1,0]);
+    % Uses the identity:
+    % inv(B^T * B) = [aa ab.cos(gamma) ac.cos(beta);
+    %                 ab.cos(gamma) bb bc.cos(alpha);
+    %                 ac.cos(beta) bc.cos(alpha) cc];
+    bb = inv(win' * win);
+    alatt = sqrt(diag(bb));
+    angdeg(1) = acos(bb(2,3) / prod(alatt(2:3)));
+    angdeg(2) = acos(bb(1,3) / prod(alatt([1 3])));
+    angdeg(3) = acos(bb(1,2) / prod(alatt(1:2)));
+    proj.alatt = 2*pi * alatt;
+    proj.angdeg = angdeg * 180 / pi;
+    self.proj_ = proj;
 else
-    self.hkl_to_Qmat_ = win.proj.bmatrix();
+    self.proj_ = win.proj;
 end
 
-
 fint = @(h,k,l,en,argi)form_factor(self,h,k,l,en,argi);