diff --git a/string.c b/string.c
index 0a5f802452..c065a8e2b6 100644
--- a/string.c
+++ b/string.c
@@ -2451,6 +2451,7 @@ str_substr(VALUE str, long beg, long len, int empty)
 	str2 = str_new_shared(rb_obj_class(str2), str2);
 	RSTRING(str2)->as.heap.ptr += ofs;
 	RSTRING(str2)->as.heap.len = len;
+	ENC_CODERANGE_CLEAR(str2);
     }
     else {
 	if (!len && !empty) return Qnil;
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 6a055f1330..a375ff5de8 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -2569,6 +2569,12 @@ CODE
     assert_equal("\u3042", "\u3042\u3043".chr)
     assert_equal('', ''.chr)
   end
+
+  def test_substr_code_range
+    data = "\xff" + "a"*200
+    assert_not_predicate(data, :valid_encoding?)
+    assert_predicate(data[100..-1], :valid_encoding?)
+  end
 end
 
 class TestString2 < TestString
diff --git a/version.h b/version.h
index 6c44937809..7c9e0c5b4e 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.4.4"
 #define RUBY_RELEASE_DATE "2018-03-21"
-#define RUBY_PATCHLEVEL 278
+#define RUBY_PATCHLEVEL 279
 
 #define RUBY_RELEASE_YEAR 2018
 #define RUBY_RELEASE_MONTH 3