diff --git a/payload_consumer/filesystem_verifier_action.cc b/payload_consumer/filesystem_verifier_action.cc
index 2934fb7..45faebb7 100644
--- a/payload_consumer/filesystem_verifier_action.cc
+++ b/payload_consumer/filesystem_verifier_action.cc
@@ -456,7 +456,7 @@
   }
 }
 
-size_t FilesystemVerifierAction::GetPartitionSize() const {
+uint64_t FilesystemVerifierAction::GetPartitionSize() const {
   const InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];
   switch (verifier_step_) {
diff --git a/payload_consumer/filesystem_verifier_action.h b/payload_consumer/filesystem_verifier_action.h
index 5bc44b1..79ef64f 100644
--- a/payload_consumer/filesystem_verifier_action.h
+++ b/payload_consumer/filesystem_verifier_action.h
@@ -109,7 +109,7 @@
 
   bool IsVABC(const InstallPlan::Partition& partition) const;
 
-  size_t GetPartitionSize() const;
+  uint64_t GetPartitionSize() const;
 
   // When the read is done, finalize the hash checking of the current partition
   // and continue checking the next one.