diff --git a/unittest/force-styles/tests/improper-fourier.yaml b/unittest/force-styles/tests/improper-fourier.yaml
index 278698a190..096d9c0fa1 100644
--- a/unittest/force-styles/tests/improper-fourier.yaml
+++ b/unittest/force-styles/tests/improper-fourier.yaml
@@ -13,7 +13,11 @@ improper_style: fourier
 improper_coeff: ! |
   1  75.0 0.9 0.2 0.3 1
   2  45.0 0.5 0.1 0.8 0
-extract: ! ""
+extract: ! |
+  k 1
+  C0 1
+  C1 1
+  C2 1
 natoms: 29
 init_energy: 376.7915390602297
 init_stress: ! |2-