diff --git a/cf/broken-realloc.m4 b/cf/broken-realloc.m4
new file mode 100644
index 000000000..0de8afb4d
--- /dev/null
+++ b/cf/broken-realloc.m4
@@ -0,0 +1,26 @@
+dnl
+dnl $Id$
+dnl
+dnl Test for realloc that doesn't handle NULL as first parameter
+dnl
+AC_DEFUN(rk_BROKEN_REALLOC, [
+AC_CACHE_CHECK(if realloc if broken, ac_cv_func_realloc_broken, [
+ac_cv_func_realloc_broken=no
+AC_TRY_RUN([
+#include <stddef.h>
+#include <stdlib.h>
+
+int main()
+{
+	return realloc(NULL, 17) == NULL;
+}
+],:, ac_cv_func_realloc_broken=yes, :)
+])
+if test "$ac_cv_func_realloc_broken" = yes ; then
+	AC_DEFINE(BROKEN_REALLOC, 1, [Define if realloc(NULL) doesn't work.])
+fi
+AH_BOTTOM([#ifdef BROKEN_REALLOC
+#define realloc(X, Y) isoc_realloc((X), (Y))
+#define isoc_realloc(X, Y) ((X) ? realloc((X), (Y)) : malloc(Y))
+#endif])
+])