diff --git a/Adafruit_Sensor.h b/Adafruit_Sensor.h
index e6b2c3d..7742afc 100644
--- a/Adafruit_Sensor.h
+++ b/Adafruit_Sensor.h
@@ -144,8 +144,8 @@ class Adafruit_Sensor {
 
   // These must be defined by the subclass
   virtual void enableAutoRange(bool enabled) {};
-  virtual bool getEvent(sensors_event_t*);
-  virtual void getSensor(sensor_t*);
+  virtual bool getEvent(sensors_event_t*) = 0;
+  virtual void getSensor(sensor_t*) = 0;
   
  private:
   bool _autoRange;