diff --git a/ChangeLog b/ChangeLog
index 2d1618d1f3..f68fc81a4e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Mar 15 20:32:57 2016  Tanaka Akira  <akr@fsij.org>
+
+	* enum.c (enum_inject): Implement the specialied code for :+ operator
+	  for Fixnums.
+
 Tue Mar 15 20:21:01 2016  Tanaka Akira  <akr@fsij.org>
 
 	* enum.c (enum_inject): Implement the specialized code for self is an
diff --git a/enum.c b/enum.c
index 49cd8ef7af..ba444e33c6 100644
--- a/enum.c
+++ b/enum.c
@@ -719,6 +719,17 @@ enum_inject(int argc, VALUE *argv, VALUE obj)
             i = 0;
         }
         id = SYM2ID(op);
+        if (id == idPLUS && FIXNUM_P(v)) {
+            long n = FIX2LONG(v);
+            while (i < RARRAY_LEN(obj)) {
+                VALUE e = RARRAY_AREF(obj, i);
+                if (!FIXNUM_P(e)) break;
+                n += FIX2LONG(e); /* should not overflow long type */
+                i++;
+                if (!FIXABLE(n)) break;
+            }
+            v = LONG2NUM(n);
+        }
         for (; i<RARRAY_LEN(obj); i++) {
             v = rb_funcall(v, id, 1, RARRAY_AREF(obj, i));
         }