diff --git a/patches/pkgbuild/gcc.sh b/patches/pkgbuild/gcc.sh
index 8af489e..b22f87d 100755
--- a/patches/pkgbuild/gcc.sh
+++ b/patches/pkgbuild/gcc.sh
@@ -182,3 +182,22 @@ else
     echo "gcc: libgccjit ENABLED (second full build of the tree)"
 fi
 echo "gcc: front ends reduced, multilib off, lib32 removed"
+# Bound the parallelism of gcc's own bootstrap, INSIDE the PKGBUILD.
+#
+# With MAKEFLAGS=-j16 the stage-2 bootstrap raced against itself:
+#
+#   /usr/include/strings.h:23:10: fatal error:
+#     .../gcc-build/prev-gcc/include/stddef.h: No such file or directory
+#
+# The file was PRESENT when the tree was inspected afterwards. It is not
+# missing -- it is generated by a rule another rule consumes without
+# declaring the dependency, and sixteen jobs win that race often enough to
+# fail. Read as an absent header, it sends you hunting through include paths
+# for nothing.
+#
+# The setting has to go into build(): this hook runs in its own bash process,
+# so exporting MAKEFLAGS here would never reach makepkg. gcc is the only
+# package in the list that bootstraps itself three times, so the bound is
+# applied here rather than globally.
+sed -i '0,/^build() {$/s//build() {\n  export MAKEFLAGS="-j8"/' PKGBUILD
+grep -A1 '^build() {' PKGBUILD | head -2 | sed 's/^/  /'