diff --git a/payload_generator/generate_delta_main.cc b/payload_generator/generate_delta_main.cc
index 7c304ce..bef09bb 100644
--- a/payload_generator/generate_delta_main.cc
+++ b/payload_generator/generate_delta_main.cc
@@ -54,13 +54,13 @@
 namespace {
 
 void ParseSignatureSizes(const string& signature_sizes_flag,
-                         vector<int>* signature_sizes) {
+                         vector<size_t>* signature_sizes) {
   signature_sizes->clear();
   vector<string> split_strings = base::SplitString(
       signature_sizes_flag, ":", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
   for (const string& str : split_strings) {
-    int size = 0;
-    bool parsing_successful = base::StringToInt(str, &size);
+    size_t size = 0;
+    bool parsing_successful = base::StringToSizeT(str, &size);
     LOG_IF(FATAL, !parsing_successful) << "Invalid signature size: " << str;
 
     LOG_IF(FATAL, size != 256 && size != 512)
@@ -102,7 +102,7 @@
   return true;
 }
 
-void CalculateHashForSigning(const vector<int>& sizes,
+void CalculateHashForSigning(const vector<size_t>& sizes,
                              const string& out_hash_file,
                              const string& out_metadata_hash_file,
                              const string& in_file) {
@@ -445,8 +445,10 @@
   // Initialize the Xz compressor.
   XzCompressInit();
 
-  vector<int> signature_sizes;
-  ParseSignatureSizes(FLAGS_signature_size, &signature_sizes);
+  vector<size_t> signature_sizes;
+  if (!FLAGS_signature_size.empty()) {
+    ParseSignatureSizes(FLAGS_signature_size, &signature_sizes);
+  }
 
   if (!FLAGS_out_hash_file.empty() || !FLAGS_out_metadata_hash_file.empty()) {
     CHECK(FLAGS_out_metadata_size_file.empty());
diff --git a/payload_generator/payload_signer.cc b/payload_generator/payload_signer.cc
index 92313dc..9739052 100644
--- a/payload_generator/payload_signer.cc
+++ b/payload_generator/payload_signer.cc
@@ -352,7 +352,7 @@
 }
 
 bool PayloadSigner::HashPayloadForSigning(const string& payload_path,
-                                          const vector<int>& signature_sizes,
+                                          const vector<size_t>& signature_sizes,
                                           brillo::Blob* out_payload_hash_data,
                                           brillo::Blob* out_metadata_hash) {
   // Create a signature blob with signatures filled with 0.
diff --git a/payload_generator/payload_signer.h b/payload_generator/payload_signer.h
index 7854e12..76e583b 100644
--- a/payload_generator/payload_signer.h
+++ b/payload_generator/payload_signer.h
@@ -91,7 +91,7 @@
   //
   // The changes to payload are not preserved or written to disk.
   static bool HashPayloadForSigning(const std::string& payload_path,
-                                    const std::vector<int>& signature_sizes,
+                                    const std::vector<size_t>& signature_sizes,
                                     brillo::Blob* out_payload_hash_data,
                                     brillo::Blob* out_metadata_hash);
 
diff --git a/payload_generator/payload_signer_unittest.cc b/payload_generator/payload_signer_unittest.cc
index 75fc694..eaf8776 100644
--- a/payload_generator/payload_signer_unittest.cc
+++ b/payload_generator/payload_signer_unittest.cc
@@ -171,7 +171,7 @@
   uint64_t metadata_size;
   EXPECT_TRUE(payload.WritePayload(
       payload_file.path(), "/dev/null", "", &metadata_size));
-  const vector<int> sizes = {256};
+  const vector<size_t> sizes = {256};
   brillo::Blob unsigned_payload_hash, unsigned_metadata_hash;
   EXPECT_TRUE(PayloadSigner::HashPayloadForSigning(payload_file.path(),
                                                    sizes,