diff --git a/m4/jm-glibc-io.m4 b/m4/jm-glibc-io.m4
new file mode 100644
index 000000000..e8054f0bd
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+++ b/m4/jm-glibc-io.m4
@@ -0,0 +1,14 @@
+#serial 7 -*- autoconf -*-
+
+dnl From Jim Meyering.
+dnl
+dnl See if the glibc *_unlocked I/O macros are available.
+dnl Use only those *_unlocked macros that are declared.
+dnl
+
+AC_DEFUN([jm_FUNC_GLIBC_UNLOCKED_IO],
+  [AC_CHECK_DECLS(
+     [clearerr_unlocked, feof_unlocked, ferror_unlocked,
+      fflush_unlocked, fgets_unlocked, fputc_unlocked, fputs_unlocked,
+      fread_unlocked, fwrite_unlocked, getc_unlocked,
+      getchar_unlocked, putc_unlocked, putchar_unlocked])])