diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 5a7c63e64381e48a193610305973c468502565d2..65b837e96fe629d58f539b253dc1ab14595a459b 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -8280,7 +8280,7 @@ enum {
 
 /* MIPI DSI registers */
 
-#define _MIPI_PORT(port, a, c)	((port) ? c : a)	/* ports A and C only */
+#define _MIPI_PORT(port, a, c)	(((port) == PORT_A) ? a : c)	/* ports A and C only */
 #define _MMIO_MIPI(port, a, c)	_MMIO(_MIPI_PORT(port, a, c))
 
 #define MIPIO_TXESC_CLK_DIV1			_MMIO(0x160004)