diff --git a/drivers/infiniband/hw/mthca/mthca_cmd.c b/drivers/infiniband/hw/mthca/mthca_cmd.c
index acc95892713a..6966f943f440 100644
--- a/drivers/infiniband/hw/mthca/mthca_cmd.c
+++ b/drivers/infiniband/hw/mthca/mthca_cmd.c
@@ -290,6 +290,12 @@ static int mthca_cmd_post(struct mthca_dev *dev,
 		err = mthca_cmd_post_hcr(dev, in_param, out_param, in_modifier,
 					 op_modifier, op, token, event);
 
+	/*
+	 * Make sure that our HCR writes don't get mixed in with
+	 * writes from another CPU starting a FW command.
+	 */
+	mmiowb();
+
 	mutex_unlock(&dev->cmd.hcr_mutex);
 	return err;
 }