diff --git a/m4/jm-glibc-io.m4 b/m4/jm-glibc-io.m4
new file mode 100644
index 000000000..e6ff4daa2
--- /dev/null
+++ b/m4/jm-glibc-io.m4
@@ -0,0 +1,24 @@
+#serial 1
+
+dnl From Jim Meyering.
+dnl
+dnl See if the glibc *_unlocked I/O macros are available.
+dnl
+
+AC_DEFUN(jm_FUNC_GLIBC_UNLOCKED_IO,
+  [AC_CHECK_FUNCS(				\
+    clearerr_unlocked				\
+    fclose_unlocked				\
+    feof_unlocked				\
+    ferror_unlocked				\
+    fflush_unlocked				\
+    fputc_unlocked				\
+    fread_unlocked				\
+    fwrite_unlocked				\
+    getc_unlocked				\
+    getchar_unlocked				\
+    putc_unlocked				\
+    putchar_unlocked				\
+   )
+  ]
+)