diff --git a/libc/malloc.cpp b/libc/malloc.cpp
index c1ac4eb636..80c9254fdf 100644
--- a/libc/malloc.cpp
+++ b/libc/malloc.cpp
@@ -54,10 +54,12 @@ static bool allocate_pool(size_t pool_index)
 	assert(pool.start == nullptr);
 
 	// allocate memory for pool
-	pool.start = (uint8_t*)mmap(nullptr, pool.size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
-	if (pool.start == nullptr)
+	void* new_pool = mmap(nullptr, pool.size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (new_pool == MAP_FAILED)
 		return false;
 
+	pool.start = (uint8_t*)new_pool;
+
 	// initialize pool to single unallocated node
 	auto* node = (malloc_node_t*)pool.start;
 	node->allocated = false;
diff --git a/libc/sys/mman.cpp b/libc/sys/mman.cpp
index c34e65f2cd..73ad1d72ab 100644
--- a/libc/sys/mman.cpp
+++ b/libc/sys/mman.cpp
@@ -13,7 +13,7 @@ void* mmap(void* addr, size_t len, int prot, int flags, int fildes, off_t off)
 	};
 	long ret = syscall(SYS_MMAP, &args);
 	if (ret == -1)
-		return nullptr;
+		return MAP_FAILED;
 	return (void*)ret;
 }