diff --git a/build/gen.py b/build/gen.py
index 9a9027b..c95b57e 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -924,6 +924,7 @@
         'src/gn/string_output_buffer_unittest.cc',
         'src/gn/string_utils_unittest.cc',
         'src/gn/substitution_pattern_unittest.cc',
+        'src/gn/substitution_type_unittest.cc',
         'src/gn/substitution_writer_unittest.cc',
         'src/gn/target_public_pair_unittest.cc',
         'src/gn/target_unittest.cc',
diff --git a/src/gn/substitution_type.cc b/src/gn/substitution_type.cc
index 723bf8a..9f7877f 100644
--- a/src/gn/substitution_type.cc
+++ b/src/gn/substitution_type.cc
@@ -7,6 +7,9 @@
 #include <stddef.h>
 #include <stdlib.h>
 
+#include <algorithm>
+#include <cstring>
+
 #include "gn/c_substitution_type.h"
 #include "gn/err.h"
 #include "gn/rust_substitution_type.h"
@@ -123,6 +126,13 @@
   for (const Substitution* s : used) {
     vect->push_back(s);
   }
+  // Sort by name for deterministic output across different builds of the
+  // same GN source. The flat_set iterates by pointer address which can
+  // vary between binaries.
+  std::sort(vect->begin(), vect->end(),
+            [](const Substitution* a, const Substitution* b) {
+              return std::strcmp(a->name, b->name) < 0;
+            });
 }
 
 bool SubstitutionIsInOutputDir(const Substitution* type) {
diff --git a/src/gn/substitution_type_unittest.cc b/src/gn/substitution_type_unittest.cc
new file mode 100644
index 0000000..d8e8b33
--- /dev/null
+++ b/src/gn/substitution_type_unittest.cc
@@ -0,0 +1,33 @@
+// Copyright 2026 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "gn/substitution_type.h"
+
+#include <cstring>
+#include <vector>
+
+#include "util/test/test.h"
+
+TEST(SubstitutionBitsTest, FillVectorDeterministicOrdering) {
+  SubstitutionBits bits;
+  bits.used.insert(&SubstitutionTargetGenDir);
+  bits.used.insert(&SubstitutionSource);
+  bits.used.insert(&SubstitutionOutput);
+  bits.used.insert(&SubstitutionLabel);
+  bits.used.insert(&SubstitutionBundleRootDir);
+
+  std::vector<const Substitution*> vect;
+  bits.FillVector(&vect);
+
+  ASSERT_EQ(5u, vect.size());
+  EXPECT_STREQ("{{bundle_root_dir}}", vect[0]->name);
+  EXPECT_STREQ("{{label}}", vect[1]->name);
+  EXPECT_STREQ("{{output}}", vect[2]->name);
+  EXPECT_STREQ("{{source}}", vect[3]->name);
+  EXPECT_STREQ("{{target_gen_dir}}", vect[4]->name);
+
+  for (size_t i = 1; i < vect.size(); ++i) {
+    EXPECT_LT(std::strcmp(vect[i - 1]->name, vect[i]->name), 0);
+  }
+}