diff --git a/include/linux/mfd/macsmc.h b/include/linux/mfd/macsmc.h
index 6b13f01a8592..f6f80c33b5cf 100644
--- a/include/linux/mfd/macsmc.h
+++ b/include/linux/mfd/macsmc.h
@@ -41,6 +41,7 @@ typedef u32 smc_key;
  */
 #define SMC_KEY(s) (smc_key)(_SMC_KEY(#s))
 #define _SMC_KEY(s) (((s)[0] << 24) | ((s)[1] << 16) | ((s)[2] << 8) | (s)[3])
+#define __SMC_KEY(a, b, c, d) (((u32)(a) << 24) | ((u32)(b) << 16) | ((u32)(c) << 8) | ((u32)(d)))
 
 #define APPLE_SMC_READABLE BIT(7)
 #define APPLE_SMC_WRITABLE BIT(6)