diff -r a602dc132c2d libgo/mksysinfo.sh
--- a/libgo/mksysinfo.sh	Tue Aug 14 20:46:42 2012 -0700
+++ b/libgo/mksysinfo.sh	Mon Aug 20 22:10:34 2012 -0700
@@ -211,6 +211,16 @@
   echo "const O_CLOEXEC = 0" >> ${OUT}
 fi
 
+# These flags can be lost on i386 GNU/Linux when using
+# -D_FILE_OFFSET_BITS=64, because we see "#define F_SETLK F_SETLK64"
+# before we see the definition of F_SETLK64.
+for flag in F_GETLK F_SETLK F_SETLKW; do
+  if ! grep "^const ${flag} " ${OUT} >/dev/null 2>&1 \
+      && grep "^const ${flag}64 " ${OUT} >/dev/null 2>&1; then
+    echo "const ${flag} = ${flag}64" >> ${OUT}
+  fi
+done
+
 # The signal numbers.
 grep '^const _SIG[^_]' gen-sysinfo.go | \
   grep -v '^const _SIGEV_' | \