diff --git a/array.c b/array.c
index ecf1fed5c1..f8faf697bf 100644
--- a/array.c
+++ b/array.c
@@ -1994,7 +1994,10 @@ ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first)
 	if (RB_TYPE_P(val, T_STRING)) {
 	  str_join:
 	    rb_str_buf_append(result, val);
-	    *first = FALSE;
+	    if (*first) {
+		rb_enc_copy(result, val);
+		*first = FALSE;
+	    }
 	}
 	else if (RB_TYPE_P(val, T_ARRAY)) {
 	    obj = val;
@@ -2025,10 +2028,6 @@ ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first)
 		goto ary_join;
 	    }
 	    val = rb_obj_as_string(val);
-	    if (*first) {
-		rb_enc_copy(result, val);
-		*first = FALSE;
-	    }
 	    goto str_join;
 	}
     }
diff --git a/test/ruby/test_array.rb b/test/ruby/test_array.rb
index 5bd4517f2e..e7e654d181 100644
--- a/test/ruby/test_array.rb
+++ b/test/ruby/test_array.rb
@@ -1085,6 +1085,7 @@ class TestArray < Test::Unit::TestCase
     assert_equal(Encoding::US_ASCII, [1, [u]].join.encoding)
     assert_equal(Encoding::UTF_8, [u, [e]].join.encoding)
     assert_equal(Encoding::UTF_8, [u, [1]].join.encoding)
+    assert_equal(Encoding::UTF_8, [Struct.new(:to_str).new(u)].join.encoding)
     bug5379 = '[ruby-core:39776]'
     assert_equal(Encoding::US_ASCII, [[], u, nil].join.encoding, bug5379)
     assert_equal(Encoding::UTF_8, [[], "\u3042", nil].join.encoding, bug5379)