diff --git a/src/tag.cpp b/src/tag.cpp
index 35a1b46..9d36317 100644
--- a/src/tag.cpp
+++ b/src/tag.cpp
@@ -29,7 +29,7 @@ Tag::Tag(const Token& token)
   }
 }
 
-std::string Tag::Translate(const Directives& directives) {
+std::string Tag::Translate(const Directives& directives) const {
   switch (type) {
     case VERBATIM:
       return value;
diff --git a/src/tag.h b/src/tag.h
index c811f39..efa77f0 100644
--- a/src/tag.h
+++ b/src/tag.h
@@ -23,7 +23,7 @@ struct Tag {
   };
 
   Tag(const Token& token);
-  std::string Translate(const Directives& directives);
+  std::string Translate(const Directives& directives) const;
 
   TYPE type;
   std::string handle, value;