diff --git a/ChangeLog b/ChangeLog
index a517a2808a..34ccc15de9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Wed Aug 12 Wed Aug 12 14:54:34 2009  Koichi Sasada  <ko1@atdot.net>
+
+	* insns.def, vm.c, vm_insnhelper.c, vm_insnhelper.h: check
+	  definition of (classes)#=== for case/when optimization.
+	  Fix Bug #1376 [ruby-core:23190].
+
+	* string.c (Init_String), bignum.c (Init_Bignum),
+	  numeric.c (Init_Numeric): define String#===, Symbol#===,
+	  Bignum#===, Fixnum#===, Float#=== as same as (classes)#==.
+
 Wed Aug 12 14:14:42 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/win32.c (readdir_internal): free old temporary filename.
diff --git a/bignum.c b/bignum.c
index 00433cc40d..f2104f042c 100644
--- a/bignum.c
+++ b/bignum.c
@@ -3253,6 +3253,7 @@ Init_Bignum(void)
 
     rb_define_method(rb_cBignum, "<=>", rb_big_cmp, 1);
     rb_define_method(rb_cBignum, "==", rb_big_eq, 1);
+    rb_define_method(rb_cBignum, "===", rb_big_eq, 1);
     rb_define_method(rb_cBignum, "eql?", rb_big_eql, 1);
     rb_define_method(rb_cBignum, "hash", rb_big_hash, 0);
     rb_define_method(rb_cBignum, "to_f", rb_big_to_f, 0);
diff --git a/insns.def b/insns.def
index 98f0dcd14c..dfae799b30 100644
--- a/insns.def
+++ b/insns.def
@@ -1233,10 +1233,7 @@ opt_case_dispatch
 (..., VALUE key)
 () // inc += -1;
 {
-    if (0) {
-	/* TODO: if some === method is overrided */
-    }
-    else {
+    if (BASIC_OP_UNREDEFINED_P(BOP_EQQ)) {
 	VALUE val;
 	if (st_lookup(RHASH_TBL(hash), key, &val)) {
 	    JUMP(FIX2INT(val));
@@ -1245,6 +1242,20 @@ opt_case_dispatch
 	    JUMP(else_offset);
 	}
     }
+    else {
+	struct opt_case_dispatch_i_arg arg = {
+	    key, -1
+	};
+
+	st_foreach(RHASH_TBL(hash), opt_case_dispatch_i, &arg);
+
+	if (arg.label != -1) {
+	    JUMP(arg.label);
+	}
+	else {
+	    JUMP(else_offset);
+	}
+    }
 }
 
 /**
diff --git a/numeric.c b/numeric.c
index 3c64fc81c1..ecaf9c503b 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3222,6 +3222,7 @@ Init_Numeric(void)
     rb_define_method(rb_cFixnum, "magnitude", fix_abs, 0);
 
     rb_define_method(rb_cFixnum, "==", fix_equal, 1);
+    rb_define_method(rb_cFixnum, "===", fix_equal, 1);
     rb_define_method(rb_cFixnum, "<=>", fix_cmp, 1);
     rb_define_method(rb_cFixnum, ">",  fix_gt, 1);
     rb_define_method(rb_cFixnum, ">=", fix_ge, 1);
@@ -3275,6 +3276,7 @@ Init_Numeric(void)
     rb_define_method(rb_cFloat, "divmod", flo_divmod, 1);
     rb_define_method(rb_cFloat, "**", flo_pow, 1);
     rb_define_method(rb_cFloat, "==", flo_eq, 1);
+    rb_define_method(rb_cFloat, "===", flo_eq, 1);
     rb_define_method(rb_cFloat, "<=>", flo_cmp, 1);
     rb_define_method(rb_cFloat, ">",  flo_gt, 1);
     rb_define_method(rb_cFloat, ">=", flo_ge, 1);
diff --git a/string.c b/string.c
index 39df54b195..7ac3bc6af9 100644
--- a/string.c
+++ b/string.c
@@ -7418,6 +7418,7 @@ Init_String(void)
     rb_define_method(rb_cString, "initialize_copy", rb_str_replace, 1);
     rb_define_method(rb_cString, "<=>", rb_str_cmp_m, 1);
     rb_define_method(rb_cString, "==", rb_str_equal, 1);
+    rb_define_method(rb_cString, "===", rb_str_equal, 1);
     rb_define_method(rb_cString, "eql?", rb_str_eql, 1);
     rb_define_method(rb_cString, "hash", rb_str_hash_m, 0);
     rb_define_method(rb_cString, "casecmp", rb_str_casecmp, 1);
@@ -7547,6 +7548,7 @@ Init_String(void)
     rb_define_singleton_method(rb_cSymbol, "all_symbols", rb_sym_all_symbols, 0); /* in parse.y */
 
     rb_define_method(rb_cSymbol, "==", sym_equal, 1);
+    rb_define_method(rb_cSymbol, "===", sym_equal, 1);
     rb_define_method(rb_cSymbol, "inspect", sym_inspect, 0);
     rb_define_method(rb_cSymbol, "to_s", rb_sym_to_s, 0);
     rb_define_method(rb_cSymbol, "id2name", rb_sym_to_s, 0);
diff --git a/vm.c b/vm.c
index 2a1a98198c..c84c0c8263 100644
--- a/vm.c
+++ b/vm.c
@@ -968,6 +968,7 @@ vm_init_redefined_flag(void)
     OP(DIV, DIV), (C(Fixnum), C(Float));
     OP(MOD, MOD), (C(Fixnum), C(Float));
     OP(Eq, EQ), (C(Fixnum), C(Float), C(String));
+    OP(Eqq, EQQ), (C(Fixnum), C(Bignum), C(Float), C(Symbol), C(String));
     OP(LT, LT), (C(Fixnum));
     OP(LE, LE), (C(Fixnum));
     OP(LTLT, LTLT), (C(String), C(Array));
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 3053fda1de..07aa24468b 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1592,3 +1592,21 @@ opt_eq_func(VALUE recv, VALUE obj, IC ic)
 
     return val;
 }
+
+struct opt_case_dispatch_i_arg {
+    VALUE obj;
+    int label;
+};
+
+static int
+opt_case_dispatch_i(st_data_t key, st_data_t data, struct opt_case_dispatch_i_arg *arg)
+{
+    if (RTEST(rb_funcall((VALUE)key, idEqq, 1, arg->obj))) {
+	arg->label = FIX2INT((VALUE)data);
+	return ST_STOP;
+    }
+    else {
+	return ST_CONTINUE;
+    }
+}
+
diff --git a/vm_insnhelper.h b/vm_insnhelper.h
index a6d3f0469d..d40f3de0a0 100644
--- a/vm_insnhelper.h
+++ b/vm_insnhelper.h
@@ -41,6 +41,7 @@ enum {
   BOP_DIV,
   BOP_MOD,
   BOP_EQ,
+  BOP_EQQ,
   BOP_LT,
   BOP_LE,
   BOP_LTLT,