diff --git a/lib/page_alloc.c b/lib/page_alloc.c
index d068fb94..3a40aa8f 100644
--- a/lib/page_alloc.c
+++ b/lib/page_alloc.c
@@ -46,15 +46,15 @@ void *__ihk_pagealloc_init(unsigned long start, unsigned long size,
 	} else {
 		desc = (void *)allocate_pages(descsize, 0);
 	}
-	flag = descsize;
-	memset(desc, 0, descsize * PAGE_SIZE);
-
 	if (!desc) {
 		kprintf("IHK: failed to allocate page-allocator-desc "\
 		        "(%lx, %lx, %lx)\n", start, size, unit);
 		return NULL;
 	}
 
+	flag = descsize;
+	memset(desc, 0, descsize * PAGE_SIZE);
+
 	desc->start = start;
 	desc->last = 0;
 	desc->count = mapaligned >> 3;