diff --git a/ext/date/date_core.c b/ext/date/date_core.c
index 457838e41f8d55..e4021051731714 100644
--- a/ext/date/date_core.c
+++ b/ext/date/date_core.c
@@ -4464,11 +4464,10 @@ get_limit(VALUE opt)
 #define rb_category_warn(category, fmt) rb_warn(fmt)
 #endif
 
-static void
+static VALUE
 check_limit(VALUE str, VALUE opt)
 {
     size_t slen, limit;
-    if (NIL_P(str)) return;
     StringValue(str);
     slen = RSTRING_LEN(str);
     limit = get_limit(opt);
@@ -4476,6 +4475,7 @@ check_limit(VALUE str, VALUE opt)
 	rb_raise(rb_eArgError,
 		 "string length (%"PRI_SIZE_PREFIX"u) exceeds the limit %"PRI_SIZE_PREFIX"u", slen, limit);
     }
+    return str;
 }
 
 static VALUE
@@ -4484,8 +4484,7 @@ date_s__parse_internal(int argc, VALUE *argv, VALUE klass)
     VALUE vstr, vcomp, hash, opt;
 
     argc = rb_scan_args(argc, argv, "11:", &vstr, &vcomp, &opt);
-    check_limit(vstr, opt);
-    StringValue(vstr);
+    vstr = check_limit(vstr, opt);
     if (!rb_enc_str_asciicompat_p(vstr))
 	rb_raise(rb_eArgError,
 		 "string should have ASCII compatible encoding");
@@ -4620,7 +4619,7 @@ date_s__iso8601(int argc, VALUE *argv, VALUE klass)
     VALUE str, opt;
 
     rb_scan_args(argc, argv, "1:", &str, &opt);
-    check_limit(str, opt);
+    if (!NIL_P(str)) str = check_limit(str, opt);
 
     return date__iso8601(str);
 }
@@ -4690,7 +4689,7 @@ date_s__rfc3339(int argc, VALUE *argv, VALUE klass)
     VALUE str, opt;
 
     rb_scan_args(argc, argv, "1:", &str, &opt);
-    check_limit(str, opt);
+    if (!NIL_P(str)) str = check_limit(str, opt);
 
     return date__rfc3339(str);
 }
@@ -4759,7 +4758,7 @@ date_s__xmlschema(int argc, VALUE *argv, VALUE klass)
     VALUE str, opt;
 
     rb_scan_args(argc, argv, "1:", &str, &opt);
-    check_limit(str, opt);
+    if (!NIL_P(str)) str = check_limit(str, opt);
 
     return date__xmlschema(str);
 }
@@ -4828,7 +4827,7 @@ date_s__rfc2822(int argc, VALUE *argv, VALUE klass)
     VALUE str, opt;
 
     rb_scan_args(argc, argv, "1:", &str, &opt);
-    check_limit(str, opt);
+    if (!NIL_P(str)) str = check_limit(str, opt);
 
     return date__rfc2822(str);
 }
@@ -4896,7 +4895,7 @@ date_s__httpdate(int argc, VALUE *argv, VALUE klass)
     VALUE str, opt;
 
     rb_scan_args(argc, argv, "1:", &str, &opt);
-    check_limit(str, opt);
+    if (!NIL_P(str)) str = check_limit(str, opt);
 
     return date__httpdate(str);
 }
@@ -4965,7 +4964,7 @@ date_s__jisx0301(int argc, VALUE *argv, VALUE klass)
     VALUE str, opt;
 
     rb_scan_args(argc, argv, "1:", &str, &opt);
-    check_limit(str, opt);
+    if (!NIL_P(str)) str = check_limit(str, opt);
 
     return date__jisx0301(str);
 }
diff --git a/test/date/test_date_parse.rb b/test/date/test_date_parse.rb
index cc29771cf85b22..720624c02e338b 100644
--- a/test/date/test_date_parse.rb
+++ b/test/date/test_date_parse.rb
@@ -544,6 +544,8 @@ def test__parse__2
 
     h = Date._parse('')
     assert_equal({}, h)
+
+    assert_raise(TypeError) {Date._parse(nil)}
   end
 
   def test_parse
@@ -1304,4 +1306,20 @@ def test_length_limit
 
     assert_raise(ArgumentError) { Date._parse("Jan " + "9" * 1000000) }
   end
+
+  def test_string_argument
+    s = '2001-02-03T04:05:06Z'
+    obj = Class.new(Struct.new(:to_str, :count)) do
+      def to_str
+        self.count +=1
+        super
+      end
+    end.new(s, 0)
+
+    all_assertions_foreach(nil, :_parse, :_iso8601, :_rfc3339, :_xmlschema) do |m|
+      obj.count = 0
+      assert_not_equal({}, Date.__send__(m, obj))
+      assert_equal(1, obj.count)
+    end
+  end
 end
diff --git a/test/json/json_encoding_test.rb b/test/json/json_encoding_test.rb
index 8dce81da590e76..2789e94b5b3f2b 100644
--- a/test/json/json_encoding_test.rb
+++ b/test/json/json_encoding_test.rb
@@ -35,6 +35,8 @@ def test_generate_shared_string
     # Ref: https://github.com/ruby/json/issues/859
     s = "01234567890"
     assert_equal '"234567890"', JSON.dump(s[2..-1])
+    s = '01234567890123456789"a"b"c"d"e"f"g"h'
+    assert_equal '"\"a\"b\"c\"d\"e\"f\"g\""', JSON.dump(s[20, 15])
   end
 
   def test_unicode