diff --git a/build/gen.py b/build/gen.py
index 5250954..3364cb9 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -408,6 +408,12 @@
   if not platform.is_msvc():
     if options.debug:
       cflags.extend(['-O0', '-g'])
+      # Enable libc++ or libstdc++ assertions in debug mode.
+      # Just set both macros to avoid detecting the C++ runtime being used.
+      # Currently disabled on MacOS since this results in linking errors at the
+      # moment, due to what looks like an XCode-specific Clang packaging error.
+      if not platform.is_darwin():
+        cflags.extend(['-D_LIBCPP_DEBUG=1', '-D_GLIBCXX_DEBUG=1'])
     else:
       cflags.append('-DNDEBUG')
       cflags.append('-O3')
diff --git a/src/gn/json_project_writer.cc b/src/gn/json_project_writer.cc
index a37fa9b..96ddacc 100644
--- a/src/gn/json_project_writer.cc
+++ b/src/gn/json_project_writer.cc
@@ -5,14 +5,12 @@
 #include "gn/json_project_writer.h"
 
 #include <algorithm>
-#include <fstream>
 #include <memory>
 #include <unordered_map>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
-#include "base/files/file_util.h"
 #include "base/json/json_writer.h"
 #include "base/json/string_escape.h"
 #include "base/strings/string_number_conversions.h"
@@ -73,8 +71,7 @@
     for (const auto* target : *targets)
       AddTargetDependencies(target, &target_set);
 
-    targets->clear();
-    targets->insert(targets->end(), target_set.begin(), target_set.end());
+    targets->assign(target_set.begin(), target_set.end());
   }
 
   // Sort the list of targets per-label to get a consistent ordering of them