We show that because of the milder GIM suppression, the four-quark dipenguin operator contributes to the short distance piece of theD0−D¯0mixing amplitude at the same order of magnitude as the box diagram. In addition, we put an upper bound&Dgr;mDLDR⩽5mDboxon a long-distance resonant contribution induced by the penguin mixing. ©1998 American Institute of Physics.