diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 92246619947c..4633915cb51b 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1359,7 +1359,7 @@ static inline unsigned int drm_crtc_index(const struct drm_crtc *crtc)
  * Given a registered CRTC, return the mask bit of that CRTC for an
  * encoder's possible_crtcs field.
  */
-static inline uint32_t drm_crtc_mask(struct drm_crtc *crtc)
+static inline uint32_t drm_crtc_mask(const struct drm_crtc *crtc)
 {
 	return 1 << drm_crtc_index(crtc);
 }
diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h
index 387e33a4d6ee..c7438ff0d609 100644
--- a/include/drm/drm_encoder.h
+++ b/include/drm/drm_encoder.h
@@ -189,7 +189,7 @@ static inline unsigned int drm_encoder_index(struct drm_encoder *encoder)
 }
 
 /* FIXME: We have an include file mess still, drm_crtc.h needs untangling. */
-static inline uint32_t drm_crtc_mask(struct drm_crtc *crtc);
+static inline uint32_t drm_crtc_mask(const struct drm_crtc *crtc);
 
 /**
  * drm_encoder_crtc_ok - can a given crtc drive a given encoder?