diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index de77f3b5..fd97b3ef 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -167,10 +167,12 @@ static inline bool mi_mul_overflow(size_t count, size_t size, size_t* total) {
 #endif
 }
 
-// Align upwards
-static inline uintptr_t _mi_is_power_of_two(uintptr_t x) {
+// Is `x` a power of two? 
+static inline bool _mi_is_power_of_two(uintptr_t x) {
   return ((x & (x - 1)) == 0);
 }
+
+// Align upwards
 static inline uintptr_t _mi_align_up(uintptr_t sz, size_t alignment) {
   uintptr_t mask = alignment - 1;
   if ((alignment & mask) == 0) {  // power of two?
diff --git a/src/alloc-posix.c b/src/alloc-posix.c
index f51aa999..f64cb1f6 100644
--- a/src/alloc-posix.c
+++ b/src/alloc-posix.c
@@ -48,7 +48,7 @@ int mi_posix_memalign(void** p, size_t alignment, size_t size) mi_attr_noexcept
   // <http://man7.org/linux/man-pages/man3/posix_memalign.3.html>
   if (p == NULL) return EINVAL;
   if (alignment % sizeof(void*) != 0) return EINVAL;      // natural alignment
-  if ((alignment & (alignment - 1)) != 0) return EINVAL;  // not a power of 2
+  if (!_mi_is_power_of_two(alignment)) return EINVAL;  // not a power of 2
   void* q = mi_malloc_aligned(size, alignment);
   if (q==NULL && size != 0) return ENOMEM;
   *p = q;