diff --git a/lib/colvars/colvar.cpp b/lib/colvars/colvar.cpp
index 700d3752ac..0cb5c1ebdb 100644
--- a/lib/colvars/colvar.cpp
+++ b/lib/colvars/colvar.cpp
@@ -30,6 +30,7 @@ colvar::colvar()
   after_restart = false;
   kinetic_energy = 0.0;
   potential_energy = 0.0;
+  period = 0.0;
 
 #ifdef LEPTON
   dev_null = 0.0;