diff --git a/bson/bson_test.go b/bson/bson_test.go
index 4a3465e478..b783c5cddb 100644
--- a/bson/bson_test.go
+++ b/bson/bson_test.go
@@ -584,11 +584,20 @@ func TestMapCodec(t *testing.T) {
 }
 
 func TestExtJSONEscapeKey(t *testing.T) {
-	doc := D{{Key: "\\usb#", Value: int32(1)}}
+	doc := D{
+		{
+			Key:   "\\usb#",
+			Value: int32(1),
+		},
+		{
+			Key:   "regex",
+			Value: Regex{Pattern: "ab\\\\\\\"ab", Options: "\""},
+		},
+	}
 	b, err := MarshalExtJSON(&doc, false, false)
 	noerr(t, err)
 
-	want := "{\"\\\\usb#\":1}"
+	want := `{"\\usb#":1,"regex":{"$regularExpression":{"pattern":"ab\\\\\\\"ab","options":"\""}}}`
 	if diff := cmp.Diff(want, string(b)); diff != "" {
 		t.Errorf("Marshaled documents do not match. got %v, want %v", string(b), want)
 	}
diff --git a/bson/extjson_writer.go b/bson/extjson_writer.go
index 5f231ba1c7..2d43943fa7 100644
--- a/bson/extjson_writer.go
+++ b/bson/extjson_writer.go
@@ -407,12 +407,13 @@ func (ejvw *extJSONValueWriter) WriteRegex(pattern string, options string) error
 		return err
 	}
 
+	options = sortStringAlphebeticAscending(options)
 	var buf bytes.Buffer
 	buf.WriteString(`{"$regularExpression":{"pattern":`)
 	writeStringWithEscapes(pattern, &buf, ejvw.escapeHTML)
-	buf.WriteString(`,"options":"`)
-	buf.WriteString(sortStringAlphebeticAscending(options))
-	buf.WriteString(`"}},`)
+	buf.WriteString(`,"options":`)
+	writeStringWithEscapes(options, &buf, ejvw.escapeHTML)
+	buf.WriteString(`}},`)
 
 	ejvw.buf = append(ejvw.buf, buf.Bytes()...)