diff --git a/internal/ceres/block_structure.h b/internal/ceres/block_structure.h
index f509067..2abb36a 100644
--- a/internal/ceres/block_structure.h
+++ b/internal/ceres/block_structure.h
@@ -47,7 +47,7 @@
 
 class BlockStructureProto;
 
-typedef int16 BlockSize;
+typedef int32 BlockSize;
 
 struct Block {
   Block() : size(-1), position(-1) {}