diff --git a/include/uri.hpp b/include/uri.hpp
index 18946c9..18c4efb 100644
--- a/include/uri.hpp
+++ b/include/uri.hpp
@@ -1,5 +1,5 @@
 /*  This file is part of remwharead.
- *  Copyright © 2019 tastytea <tastytea@tastytea.de>
+ *  Copyright © 2019, 2020 tastytea <tastytea@tastytea.de>
  *
  *  This program is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -42,7 +42,7 @@ struct html_extract
     string description;
     string fulltext;
 
-    explicit operator bool();
+    explicit operator bool() const;
 };
 
 /*!
@@ -60,7 +60,7 @@ struct archive_answer
     string error;
     string uri;
 
-    explicit operator bool();
+    explicit operator bool() const;
 };
 
 /*!
diff --git a/src/lib/uri.cpp b/src/lib/uri.cpp
index 58fbd41..02658de 100644
--- a/src/lib/uri.cpp
+++ b/src/lib/uri.cpp
@@ -59,12 +59,12 @@ using std::unique_ptr;
 using std::vector;
 using RegEx = Poco::RegularExpression;
 
-html_extract::operator bool()
+html_extract::operator bool() const
 {
     return successful;
 }
 
-archive_answer::operator bool()
+archive_answer::operator bool() const
 {
     return successful;
 }