diff --git a/lib/std/heap/BrkAllocator.zig b/lib/std/heap/BrkAllocator.zig
index 1f0c88635f945be4ec5708901e4b7b3ccb21bfb3..9cb18673fe38e2acb8644e8dd41c041324b986d4 100644
--- a/lib/std/heap/BrkAllocator.zig
+++ b/lib/std/heap/BrkAllocator.zig
@@ -45,7 +45,7 @@ const size_class_count = math.log2(bigpage_size) - min_class;
 /// 1 - 2 bigpages
 /// 2 - 4 bigpages
 /// etc.
-const big_size_class_count = math.log2(bigpage_count);
+const big_size_class_count = math.log2(bigpage_count) + 1;
 
 fn alloc(ctx: *anyopaque, len: usize, alignment: Alignment, return_address: usize) ?[*]u8 {
     _ = ctx;