diff --git a/sys/cpu/i386/include/segments.h b/sys/cpu/i386/include/segments.h
index 4e19db2..adfe648 100644
--- a/sys/cpu/i386/include/segments.h
+++ b/sys/cpu/i386/include/segments.h
@@ -199,7 +199,7 @@ struct region_descriptor {
 #define	SEGEX_IDT	0x02	/* interrupt descriptor table */
 #define	SEGEX_TI	0x04	/* local descriptor table */
 				/* other bits are affected descriptor index */
-#define SEGEX_IDX(s)	((s)>>3)&0x1fff)
+#define SEGEX_IDX(s)	(((s)>>3)&0x1fff)
 
 /*
  * Size of IDT table.  Theoretically we only need to cover past 0x81
diff --git a/sys/cpu/x86_64/include/segments.h b/sys/cpu/x86_64/include/segments.h
index b8dccf1..06408c3 100644
--- a/sys/cpu/x86_64/include/segments.h
+++ b/sys/cpu/x86_64/include/segments.h
@@ -210,7 +210,7 @@ struct region_descriptor {
 #define	SEGEX_IDT	0x02	/* interrupt descriptor table */
 #define	SEGEX_TI	0x04	/* local descriptor table */
 				/* other bits are affected descriptor index */
-#define SEGEX_IDX(s)	((s)>>3)&0x1fff)
+#define SEGEX_IDX(s)	(((s)>>3)&0x1fff)
 
 /*
  * Size of the IDT table.  Theoretically we only need to cover past 0x81