diff --git a/ChangeLog b/ChangeLog
index 8e7b80c001..3b96a9b842 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Fri Apr 22 20:18:40 2016  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* include/ruby/ruby.h (rb_mul_size_overflow): added to handle
+	  mul overflow efficiently.
+
+	* include/ruby/ruby.h (rb_alloc_tmp_buffer2): use rb_mul_size_overflow
+	  and avoid division where it can define DSIZE_T.
+
+	* gc.c (xmalloc2_size): moved from ruby.h and use rb_mul_size_overflow.
+
 Fri Apr 22 20:34:04 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* time.c (time_asctime): [DOC] add ctime example, not only
diff --git a/gc.c b/gc.c
index aa6770123c..d9f495ba29 100644
--- a/gc.c
+++ b/gc.c
@@ -7792,7 +7792,16 @@ objspace_xmalloc(rb_objspace_t *objspace, size_t size)
     return objspace_xmalloc0(objspace, size);
 }
 
-#define xmalloc2_size ruby_xmalloc2_size
+static inline size_t
+xmalloc2_size(const size_t count, const size_t elsize)
+{
+    size_t ret;
+    if (rb_mul_size_overflow(count, elsize, SSIZE_MAX, &ret)) {
+	ruby_malloc_size_overflow(count, elsize);
+    }
+    return ret;
+}
+
 static void *
 objspace_xmalloc2(rb_objspace_t *objspace, size_t n, size_t size)
 {
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 89bf0192c1..71e61721d2 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1618,13 +1618,23 @@ void *rb_alloc_tmp_buffer(volatile VALUE *store, long len) RUBY_ATTR_ALLOC_SIZE(
 void *rb_alloc_tmp_buffer_with_count(volatile VALUE *store, size_t len,size_t count) RUBY_ATTR_ALLOC_SIZE((2,3));
 void rb_free_tmp_buffer(volatile VALUE *store);
 NORETURN(void ruby_malloc_size_overflow(size_t, size_t));
-static inline size_t
-ruby_xmalloc2_size(const size_t count, const size_t elsize)
+#if HAVE_LONG_LONG && SIZEOF_SIZE_T * 2 <= SIZEOF_LONG_LONG
+# define DSIZE_T unsigned LONG_LONG
+#elif defined(HAVE_INT128_T)
+# define DSIZE_T uint128_t
+#endif
+static inline int
+rb_mul_size_overflow(size_t a, size_t b, size_t max, size_t *c)
 {
-    if (count > SSIZE_MAX / elsize) {
-	ruby_malloc_size_overflow(count, elsize);
-    }
-    return count * elsize;
+#ifdef DSIZE_T
+    DSIZE_T c2 = (DSIZE_T)a * (DSIZE_T)b;
+    if (UNLIKELY(c2 > max)) return 1;
+    *c = (size_t)c2;
+#else
+    if (b != 0 && UNLIKELY(a > max / b)) return 1;
+    *c = a * b;
+#endif
+    return 0;
 }
 static inline void *
 rb_alloc_tmp_buffer2(volatile VALUE *store, long count, size_t elsize)
@@ -1636,10 +1646,11 @@ rb_alloc_tmp_buffer2(volatile VALUE *store, long count, size_t elsize)
 	}
     }
     else {
-	if (UNLIKELY(cnt > (LONG_MAX - sizeof(VALUE)) / elsize)) {
-	    ruby_malloc_size_overflow(count, elsize);
+	size_t size, max = LONG_MAX - sizeof(VALUE) + 1;
+	if (UNLIKELY(rb_mul_size_overflow(count, elsize, max, &size))) {
+	    ruby_malloc_size_overflow(cnt, elsize);
 	}
-	cnt = (cnt * elsize + sizeof(VALUE) - 1) / sizeof(VALUE);
+	cnt = (size + sizeof(VALUE) - 1) / sizeof(VALUE);
     }
     return rb_alloc_tmp_buffer_with_count(store, cnt * sizeof(VALUE), cnt);
 }