diff --git a/src/new/zernike_polynomials/FT_Rc_to_Znm.m b/src/new/zernike_polynomials/FT_Rc_to_Znm.m
index 42f609e778e274517b2fcc4f8b6f12e5a1989166..12c7fdc8eb7d0032cae022c0233fc7ea39abafa5 100644
--- a/src/new/zernike_polynomials/FT_Rc_to_Znm.m
+++ b/src/new/zernike_polynomials/FT_Rc_to_Znm.m
@@ -52,9 +52,11 @@ function [A] = FT_Rc_to_Znm(Rc,R)
     % Calculate Z20 amplitude
     A(1) = (Ax+Ay)/2;
     
-    % Calculate Z22 astigmatic amplitude
-    A(2) = 2*(Ax-A(1));
-    
+    if length(Rc)>1
+        % Calculate Z22 astigmatic amplitude
+        A(2) = 2*(Ax-A(1));
+    end
+
     % Convert amplitudes to nm
     A = 1e9*A;