diff --git a/motors/usb/usb.cc b/motors/usb/usb.cc
index fb7fe9f..36c6456 100644
--- a/motors/usb/usb.cc
+++ b/motors/usb/usb.cc
@@ -91,6 +91,8 @@
 
 }  // namespace
 
+constexpr int UsbDevice::kEndpoint0MaxSize;
+
 UsbDevice::UsbDevice(int index, uint16_t vendor_id, uint16_t product_id)
     : index_(index) {
   // TODO(Brian): Pass index_ into all the register access macros. Also sort out