diff --git a/moo/lib/dic.c b/moo/lib/dic.c
index 53cd8ec..b426724 100644
--- a/moo/lib/dic.c
+++ b/moo/lib/dic.c
@@ -197,7 +197,7 @@ oops:
 	return MOO_NULL;
 }
 
-static moo_oop_association_t lookup (moo_t* moo, moo_oop_dic_t dic, const moo_oocs_t* name)
+moo_oop_association_t moo_lookupdic_noseterr (moo_t* moo, moo_oop_dic_t dic, const moo_oocs_t* name)
 {
 	/* this is special version of moo_getatsysdic() that performs
 	 * lookup using a plain string specified */
@@ -228,10 +228,22 @@ static moo_oop_association_t lookup (moo_t* moo, moo_oop_dic_t dic, const moo_oo
 	}
 
 	/* when value is MOO_NULL, perform no insertion */
-	moo_seterrbfmt (moo, MOO_ENOENT, "unable to find %.*js in a dictionary", name->len, name->ptr);
+
+	/* moo_seterrXXX() is not called here. the dictionary lookup is very frequent 
+	 * and so is lookup failure. for instance, moo_findmethod() calls this over 
+	 * a class chain. there might be a failure at each class level. it's waste to
+	 * set the error information whenever the failure occurs.
+	 * the caller of this function must set the error information upon failure */
 	return MOO_NULL;
 }
 
+static MOO_INLINE moo_oop_association_t lookup (moo_t* moo, moo_oop_dic_t dic, const moo_oocs_t* name)
+{
+	moo_oop_association_t ass = moo_lookupdic_noseterr(moo, dic, name);
+	if (!ass) moo_seterrbfmt(moo, MOO_ENOENT, "unable to find %.*js in a dictionary", name->len, name->ptr);
+	return ass;
+}
+
 moo_oop_association_t moo_putatsysdic (moo_t* moo, moo_oop_t key, moo_oop_t value)
 {
 	MOO_ASSERT (moo, MOO_CLASSOF(moo,key) == moo->_symbol);
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index 9b2155c..75266e4 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -1635,7 +1635,7 @@ static MOO_INLINE moo_oop_method_t find_method_in_class (moo_t* moo, moo_oop_cla
 	MOO_ASSERT (moo, (moo_oop_t)mthdic != moo->_nil); 
 	MOO_ASSERT (moo, MOO_CLASSOF(moo, mthdic) == moo->_method_dictionary);
 
-	ass = (moo_oop_association_t)moo_lookupdic(moo, mthdic, name);
+	ass = (moo_oop_association_t)moo_lookupdic_noseterr(moo, mthdic, name);
 	if (ass) 
 	{
 		/* found the method */
@@ -1711,7 +1711,6 @@ moo_oop_method_t moo_findmethod (moo_t* moo, moo_oop_t receiver, const moo_oocs_
 		 * otherwise c points to a class object */
 	}
 
-
 	/* [IMPORT] the method lookup logic should be the same as ciim_on_each_method() in comp.c */
 	mth = find_method_in_class_chain(moo, c, mth_type, message);
 	if (mth) return mth;
diff --git a/moo/lib/gc.c b/moo/lib/gc.c
index 9bdc296..3418e20 100644
--- a/moo/lib/gc.c
+++ b/moo/lib/gc.c
@@ -1070,7 +1070,7 @@ moo_oop_t moo_shallowcopy (moo_t* moo, moo_oop_t oop)
 		total_bytes = MOO_SIZEOF(moo_obj_t) + get_payload_bytes(moo, oop);
 
 		moo_pushtmp (moo, &oop);
-		z = (moo_oop_t)moo_allocbytes (moo, total_bytes);
+		z = (moo_oop_t)moo_allocbytes(moo, total_bytes);
 		moo_poptmp(moo);
 
 		MOO_MEMCPY (z, oop, total_bytes);
diff --git a/moo/lib/moo-prv.h b/moo/lib/moo-prv.h
index b343089..2b24a93 100644
--- a/moo/lib/moo-prv.h
+++ b/moo/lib/moo-prv.h
@@ -1173,6 +1173,12 @@ moo_oop_association_t moo_getatdic (
 	moo_oop_t     key
 );
 
+moo_oop_association_t moo_lookupdic_noseterr (
+	moo_t*            moo,
+	moo_oop_dic_t     dic,
+	const moo_oocs_t* name
+);
+
 moo_oop_association_t moo_lookupdic (
 	moo_t*            moo,
 	moo_oop_dic_t     dic,