diff --git a/unittest/force-styles/tests/improper-umbrella.yaml b/unittest/force-styles/tests/improper-umbrella.yaml
index ff6822e9d8..604c039c28 100644
--- a/unittest/force-styles/tests/improper-umbrella.yaml
+++ b/unittest/force-styles/tests/improper-umbrella.yaml
@@ -13,7 +13,9 @@ improper_style: umbrella
 improper_coeff: ! |
   1  75.0 120.2
   2  45.0  59.5
-extract: ! ""
+extract: ! |
+  kw 1
+  w0 1
 natoms: 29
 init_energy: 120.51735030260785
 init_stress: ! |2-