diff --git a/ChangeLog b/ChangeLog
index 9120400c5a..168cc31cc5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jul 31 11:30:42 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/syck/rubyext.c (rb_syck_compile): expression in ASSERT() has no
+	  effect unless debug mode.
+
 Thu Jul 31 10:51:39 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* iseq.c (ruby_iseq_disasm_insn): suppress warnings on platforms which
diff --git a/ext/syck/rubyext.c b/ext/syck/rubyext.c
index c229f0d4dd..d5c6372076 100644
--- a/ext/syck/rubyext.c
+++ b/ext/syck/rubyext.c
@@ -113,7 +113,9 @@ rb_syck_compile(VALUE self, VALUE port)
     syck_parser_implicit_typing( parser, 0 );
     syck_parser_taguri_expansion( parser, 0 );
     oid = syck_parse( parser );
-    ASSERT(syck_lookup_sym( parser, oid, &data ));
+    if (!syck_lookup_sym( parser, oid, &data )) {
+	rb_raise(rb_eSyntaxError, "root node <%lx> not found", oid);
+    }
     sav = data;
 
     ret = S_ALLOCA_N( char, strlen( sav->buffer ) + 3 );