diff --git a/src/MOFFF/improper_inversion_harmonic.cpp b/src/MOFFF/improper_inversion_harmonic.cpp
index 681811594b..61180447f3 100644
--- a/src/MOFFF/improper_inversion_harmonic.cpp
+++ b/src/MOFFF/improper_inversion_harmonic.cpp
@@ -340,7 +340,7 @@ void ImproperInversionHarmonic::write_data(FILE *fp)
 void *ImproperInversionHarmonic::extract(const char *str, int &dim)
 {
   dim = 1;
-  if (strcmp(str, "kw") == 0) return (void *) kw;
+  if (strcmp(str, "k") == 0) return (void *) kw;
   if (strcmp(str, "w0") == 0) return (void *) w0;
   return nullptr;
 }