--- a/tools/metrics/BUILD.gn
+++ b/tools/metrics/BUILD.gn
@@ -45,7 +45,12 @@
   # for non-git checkouts.
   # TODO(crbug.com/329080012): Remove this once dirmd works in non-git
   # checkouts.
-  if (generate_location_tags) {
+  #
+  # Gentoo: generate_location_tags comes from the generated gclient_args.gni
+  # and stays true in release tarballs, but the histograms_xml target above is
+  # only declared when //.git exists. Mirror that guard so the dependency
+  # resolves instead of failing gn gen with "Unresolved dependencies".
+  if (generate_location_tags && path_exists("//.git")) {
     deps += [ ":histograms_xml" ]
   }
 }