diff --git a/src/generic/MassChargeInput.cpp b/src/generic/MassChargeInput.cpp
index cec53217e6..15763001bd 100644
--- a/src/generic/MassChargeInput.cpp
+++ b/src/generic/MassChargeInput.cpp
@@ -51,6 +51,8 @@ PLUMED_REGISTER_ACTION(MassChargeInput,"READ_MASS_CHARGE")
 void MassChargeInput::registerKeywords(Keywords& keys) {
   ActionShortcut::registerKeywords( keys );
   keys.add("compulsory","FILE","a pdb file that contains the masses and charges of the atoms in the beta and occupancy columns");
+  keys.addOutputComponent("mass","default","the masses of the atoms in the system");
+  keys.addOutputComponent("charges","default","the masses of the atoms in the system");
   keys.needsAction("CONSTANT");
 }