diff --git a/src/alloc-override.c b/src/alloc-override.c
index e06a3e6e..068b1fb3 100644
--- a/src/alloc-override.c
+++ b/src/alloc-override.c
@@ -136,6 +136,7 @@ int posix_memalign(void** p, size_t alignment, size_t size) {
   // The spec also dictates we should not modify `*p` on an error. (issue#27)
   // <http://man7.org/linux/man-pages/man3/posix_memalign.3.html>
   if (alignment % sizeof(void*) != 0) return EINVAL;  // no `p==NULL` check as it is declared as non-null
+  if ((alignment & (~alignment + 1)) != alignment) return EINVAL;  // not a power of 2
   void* q = mi_malloc_aligned(size, alignment);
   if (q==NULL && size != 0) return ENOMEM;
   *p = q;