diff --git a/ChangeLog b/ChangeLog
index 2240236fc9..b9f784d8fe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Aug 12 15:37:40 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* string.c (rb_str_intern): should check symbol table overflow.
+
 Tue Aug 12 15:31:04 2008  Minero Aoki  <aamine@loveruby.net>
 
 	* lib/net/http.rb (send_request_with_body): Content-Length should
diff --git a/string.c b/string.c
index e14f298cc8..ba2c454df8 100644
--- a/string.c
+++ b/string.c
@@ -5840,10 +5840,25 @@ VALUE
 rb_str_intern(VALUE s)
 {
     VALUE str = RB_GC_GUARD(s);
-    ID id;
+    VALUE sym;
+    ID id, id2;
 
     id = rb_intern_str(str);
-    return ID2SYM(id);
+    sym = ID2SYM(id);
+    id2 = SYM2ID(sym);
+    if (id != id2) {
+	char *name = rb_id2name(id2);
+
+	if (name) {
+	    rb_raise(rb_eRuntimeError, "symbol table overflow (%s given for %s)",
+		     name, RSTRING_PTR(str));
+	}
+	else {
+	    rb_raise(rb_eRuntimeError, "symbol table overflow (symbol %s)",
+		     RSTRING_PTR(str));
+	}
+    }
+    return sym;
 }