diff --git a/src/ipa/raspberrypi/cam_helper.hpp b/src/ipa/raspberrypi/cam_helper.hpp
index c3ed5362..618391e9 100644
--- a/src/ipa/raspberrypi/cam_helper.hpp
+++ b/src/ipa/raspberrypi/cam_helper.hpp
@@ -66,8 +66,8 @@ public:
 	virtual ~CamHelper();
 	void SetCameraMode(const CameraMode &mode);
 	MdParser &Parser() const { return *parser_; }
-	uint32_t ExposureLines(double exposure_us) const;
-	double Exposure(uint32_t exposure_lines) const; // in us
+	virtual uint32_t ExposureLines(double exposure_us) const;
+	virtual double Exposure(uint32_t exposure_lines) const; // in us
 	virtual uint32_t GetVBlanking(double &exposure_us, double minFrameDuration,
 				      double maxFrameDuration) const;
 	virtual uint32_t GainCode(double gain) const = 0;