diff --git a/src/DynareMain.cc b/src/DynareMain.cc
index 23fea237..f2d6182b 100644
--- a/src/DynareMain.cc
+++ b/src/DynareMain.cc
@@ -290,7 +290,7 @@ main(int argc, char **argv)
               equal_index != string::npos)
             defines.emplace_back(s.substr(2, equal_index-2), s.substr(equal_index+1));
           else
-            defines.emplace_back(s.substr(2), "1");
+            defines.emplace_back(s.substr(2), "true");
         }
       else if (s.substr(0, 2) == "-I")
         {
diff --git a/src/macro/Parser.yy b/src/macro/Parser.yy
index be7cc71e..7370324e 100644
--- a/src/macro/Parser.yy
+++ b/src/macro/Parser.yy
@@ -135,10 +135,7 @@ directive_one_line : INCLUDE expr
                    | INCLUDEPATH expr
                      { $$ = make_shared<IncludePath>($2, @$); }
                    | DEFINE symbol
-                     {
-                       auto tmp = make_shared<Real>("1", @$);
-                       $$ = make_shared<Define>($2, tmp, @$);
-                     }
+                     { $$ = make_shared<Define>($2, make_shared<Bool>(true, @$), @$); }
                    | DEFINE symbol EQUAL expr
                      { $$ = make_shared<Define>($2, $4, @$); }
                    | DEFINE function EQUAL expr