diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index ee144ec57935d92318e66949c1b33307d6f1ea95..89888adb9af170b5792593df231784234b0f3183 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -8278,7 +8278,7 @@ 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)