diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index a6b8e97755cd..a005f124d706 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -656,10 +656,16 @@ static void *get_result_buffer(struct dm_ioctl *param, size_t param_size,
 {
 	param->data_start = align_ptr(param + 1) - (void *) param;
 
-	if (param->data_start < param_size)
+	if (param->data_start < param_size) {
 		*len = param_size - param->data_start;
-	else
+	} else {
+		/*
+		 * The buffer can be as small as offsetof(*param, data), which
+		 * is less than sizeof(*param), so don't run off the end of it.
+		 */
 		*len = 0;
+		param->data_start = param_size;
+	}
 
 	return ((void *) param) + param->data_start;
 }