diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c
index 0190fce20078..5a4dbb410b71 100644
--- a/drivers/gpu/drm/drm_bufs.c
+++ b/drivers/gpu/drm/drm_bufs.c
@@ -414,6 +414,15 @@ int drm_addmap_ioctl(struct drm_device *dev, void *data,
 
 	/* avoid a warning on 64-bit, this casting isn't very nice, but the API is set so too late */
 	map->handle = (void *)(unsigned long)maplist->user_token;
+
+	/*
+	 * It appears that there are no users of this value whatsoever --
+	 * drmAddMap just discards it.  Let's not encourage its use.
+	 * (Keeping drm_addmap_core's returned mtrr value would be wrong --
+	 *  it's not a real mtrr index anymore.)
+	 */
+	map->mtrr = -1;
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index e77bd8b57df2..ffd7a7ba70d4 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -38,6 +38,9 @@
 
 #include <linux/pci.h>
 #include <linux/export.h>
+#ifdef CONFIG_X86
+#include <asm/mtrr.h>
+#endif
 
 /**
  * Get the bus id.
@@ -181,7 +184,17 @@ int drm_getmap(struct drm_device *dev, void *data,
 	map->type = r_list->map->type;
 	map->flags = r_list->map->flags;
 	map->handle = (void *)(unsigned long) r_list->user_token;
-	map->mtrr = r_list->map->mtrr;
+
+#ifdef CONFIG_X86
+	/*
+	 * There appears to be exactly one user of the mtrr index: dritest.
+	 * It's easy enough to keep it working on non-PAT systems.
+	 */
+	map->mtrr = phys_wc_to_mtrr_index(r_list->map->mtrr);
+#else
+	map->mtrr = -1;
+#endif
+
 	mutex_unlock(&dev->struct_mutex);
 
 	return 0;