diff --git a/src/EXTRA-MOLECULE/improper_ring.h b/src/EXTRA-MOLECULE/improper_ring.h
index db8a681f75..0c68b4e15a 100644
--- a/src/EXTRA-MOLECULE/improper_ring.h
+++ b/src/EXTRA-MOLECULE/improper_ring.h
@@ -33,6 +33,7 @@ class ImproperRing : public Improper {
   void write_restart(FILE *) override;
   void read_restart(FILE *) override;
   void write_data(FILE *) override;
+  void *extract(const char *, int &) override;
 
  protected:
   double *k, *chi;