diff --git a/src/macro/Directives.cc b/src/macro/Directives.cc
index 6b44c088..5e784e83 100644
--- a/src/macro/Directives.cc
+++ b/src/macro/Directives.cc
@@ -39,14 +39,8 @@ Eval::interpret(ostream &output, bool no_line_macro)
     }
 }
 
-void
-Include::interpret(ostream &output, bool no_line_macro)
-{
-  error(StackTrace("@#include", "should never be interpreted", location));
-}
-
 string
-Include::interpretAndGetName()
+Include::interpretAndGetName() const
 {
   try
     {
@@ -67,14 +61,8 @@ Include::interpretAndGetName()
   return "";
 }
 
-void
-IncludePath::interpret(ostream &output, bool no_line_macro)
-{
-error(StackTrace("@#includepath", "should never be interpreted", location));
-}
-
 string
-IncludePath::interpretAndGetPath()
+IncludePath::interpretAndGetPath() const
 {
   try
     {
diff --git a/src/macro/Directives.hh b/src/macro/Directives.hh
index 4b0d530a..57981aa9 100644
--- a/src/macro/Directives.hh
+++ b/src/macro/Directives.hh
@@ -69,8 +69,14 @@ namespace macro
   public:
     Include(ExpressionPtr expr_arg, Environment &env_arg, Tokenizer::location location_arg) :
       Directive(env_arg, move(location_arg)), expr{move(expr_arg)} { }
-    void interpret(ostream &output, bool no_line_macro) override;
-    string interpretAndGetName();
+    // Not interpretable because we want the class to be immutable (for use with shared_ptr)
+    // If it were interpretable, the name would need to be stored in a non-const variable
+    // rendering the class mutable
+    inline void interpret(ostream &output, bool no_line_macro) override
+    {
+      error(StackTrace("@#include", "should never be interpreted", location));
+    }
+    string interpretAndGetName() const;
   };
 
 
@@ -81,8 +87,14 @@ namespace macro
   public:
     IncludePath(ExpressionPtr expr_arg, Environment &env_arg, Tokenizer::location location_arg) :
       Directive(env_arg, move(location_arg)), expr{move(expr_arg)} { }
-    void interpret(ostream &output, bool no_line_macro) override;
-    string interpretAndGetPath();
+    // Not interpretable because we want the class to be immutable (for use with shared_ptr)
+    // If it were interpretable, the name would need to be stored in a non-const variable
+    // rendering the class mutable
+    inline void interpret(ostream &output, bool no_line_macro) override
+    {
+      error(StackTrace("@#includepath", "should never be interpreted", location));
+    }
+    string interpretAndGetPath() const;
   };