diff --git a/sys/sys/libkern.h b/sys/sys/libkern.h
index a10289d72dc..835e5ffaf0b 100644
--- a/sys/sys/libkern.h
+++ b/sys/sys/libkern.h
@@ -229,10 +229,7 @@ ilog2_long_long(long long n)
 
 #define	ilog2(n) (__builtin_constant_p(n) ? ilog2_const(n) : ilog2_var(n))
 #define	rounddown_pow_of_two(n)	((__typeof(n))1 << ilog2(n))
-#define	order_base_2(n) ({			\
-	__typeof(n) _n = (n);			\
-	_n == 1 ? 0 : 1 + ilog2(_n - 1);	\
-})
+#define order_base_2(n) ilog2(2*(n)-1)
 #define	roundup_pow_of_two(n)	((__typeof(n))1 << order_base_2(n))
 
 #define	bitcount64(x)	__bitcount64((uint64_t)(x))