diff --git a/configure.ac b/configure.ac
index e08860a36..cca7da7e4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1168,14 +1168,6 @@ AS_IF([test "x$enable_ruby" != "xno"],[
             AC_MSG_RESULT([-l$libruby])
             AC_CHECK_LIB([$libruby],[ruby_init],
                          [have_libruby=1],[have_libruby=])
-
-            dnl Symbols that we substitute when missing.
-            AS_IF([test -n "$have_libruby"],[
-                old_LIBS="$LIBS"
-                LIBS="$LIBS -l$libruby"
-                AC_CHECK_FUNCS([rb_hash_lookup])
-                LIBS="$old_LIBS"
-            ])
         ],[
             AC_MSG_RESULT([not found])
         ])
diff --git a/generator/ruby.ml b/generator/ruby.ml
index 27f689b34..adf1d11d7 100644
--- a/generator/ruby.ml
+++ b/generator/ruby.ml
@@ -700,6 +700,9 @@ Init__guestfs (void)
   e_Error = rb_define_class_under (m_guestfs, \"Error\", rb_eStandardError);
 
 #ifdef HAVE_RB_DEFINE_ALLOC_FUNC
+#ifndef HAVE_TYPE_RB_ALLOC_FUNC_T
+#define rb_alloc_func_t void*
+#endif
   rb_define_alloc_func (c_guestfs, (rb_alloc_func_t) ruby_guestfs_create);
 #endif
 
diff --git a/ruby/ext/guestfs/extconf.rb.in b/ruby/ext/guestfs/extconf.rb.in
index b8bd74a33..bf33af8c3 100644
--- a/ruby/ext/guestfs/extconf.rb.in
+++ b/ruby/ext/guestfs/extconf.rb.in
@@ -29,6 +29,10 @@ unless have_library("guestfs", "guestfs_create", "guestfs.h")
   raise "libguestfs not found"
 end
 
+have_func("rb_hash_lookup")
+have_func("rb_define_alloc_func")
+have_type("rb_alloc_func_t")
+
 $CFLAGS =
   "#{$CFLAGS} @CFLAGS@ -DGUESTFS_PRIVATE=1 " <<
   "@WARN_CFLAGS@ @WERROR_CFLAGS@"