diff --git a/unittest/force-styles/tests/improper-inversion_harmonic.yaml b/unittest/force-styles/tests/improper-inversion_harmonic.yaml
index 73eade4958..7697908c23 100644
--- a/unittest/force-styles/tests/improper-inversion_harmonic.yaml
+++ b/unittest/force-styles/tests/improper-inversion_harmonic.yaml
@@ -13,7 +13,9 @@ improper_style: inversion/harmonic
 improper_coeff: ! |
   1  75.0 0.1
   2  45.0 1.0
-extract: ! ""
+extract: ! |
+  kw 1
+  w0 1
 natoms: 29
 init_energy: 0.35230115027159387
 init_stress: ! |-