diff --git a/internal/ceres/block_structure.cc b/internal/ceres/block_structure.cc
index 5a1a5e1..00c4ce2 100644
--- a/internal/ceres/block_structure.cc
+++ b/internal/ceres/block_structure.cc
@@ -34,6 +34,9 @@
 namespace internal {
 
 bool CellLessThan(const Cell& lhs, const Cell& rhs) {
+  if (lhs.block_id == rhs.block_id) {
+    return (lhs.position  < rhs.position);
+  }
   return (lhs.block_id < rhs.block_id);
 }
 
diff --git a/internal/ceres/block_structure.h b/internal/ceres/block_structure.h
index 2abb36a..656716e 100644
--- a/internal/ceres/block_structure.h
+++ b/internal/ceres/block_structure.h
@@ -45,8 +45,6 @@
 namespace ceres {
 namespace internal {
 
-class BlockStructureProto;
-
 typedef int32 BlockSize;
 
 struct Block {
@@ -89,16 +87,6 @@
   vector<CompressedColumn> cols;
 };
 
-// Deserialize the given block structure proto to the given block structure.
-// Destroys previous contents of block_structure.
-void ProtoToBlockStructure(const BlockStructureProto &proto,
-                           CompressedRowBlockStructure *block_structure);
-
-// Serialize the given block structure to the given proto. Destroys previous
-// contents of proto.
-void BlockStructureToProto(const CompressedRowBlockStructure &block_structure,
-                           BlockStructureProto *proto);
-
 }  // namespace internal
 }  // namespace ceres