diff --git a/src/angle.h b/src/angle.h
index 48e8fe441b..c027ef5903 100644
--- a/src/angle.h
+++ b/src/angle.h
@@ -36,7 +36,7 @@ class Angle : protected Pointers {
   virtual double equilibrium_angle(int) = 0;
   virtual void write_restart(FILE *) = 0;
   virtual void read_restart(FILE *) = 0;
-  virtual double single(int, int, int, int, double) {return 0.0;}
+  virtual double single(int, int, int, int) = 0;
   virtual int memory_usage() {return 0;}
 };