diff --git a/m4/c-bs-a.m4 b/m4/c-bs-a.m4
new file mode 100644
index 00000000..ceb26ae5
--- /dev/null
+++ b/m4/c-bs-a.m4
@@ -0,0 +1,25 @@
+#serial 1
+
+dnl From Paul Eggert.
+
+AC_DEFUN(AC_C_BACKSLASH_A,
+[
+  AC_CACHE_CHECK([whether backslash-a works in strings], ac_cv_c_backslash_a,
+   [AC_TRY_COMPILE([],
+     [
+      changequote(, ) dnl
+#if '\a' == 'a'
+      syntax error;
+#endif
+      char buf['\a' == 'a' ? -1 : 1];
+      buf[0] = '\a';
+      return buf[0] != "\a"[0];
+      changequote([, ])dnl
+     ],
+     ac_cv_c_backslash_a=yes,
+     ac_cv_c_backslash_a=no)])
+  if test $ac_cv_c_backslash_a = yes; then
+    AC_DEFINE(HAVE_C_BACKSLASH_A, 1,
+      [Define if backslash-a works in C strings.])
+  fi
+])