diff --git a/include/plasp/pddl/Expression.h b/include/plasp/pddl/Expression.h
index 565ba1c..f430280 100644
--- a/include/plasp/pddl/Expression.h
+++ b/include/plasp/pddl/Expression.h
@@ -3,8 +3,6 @@
 
 #include <memory>
 
-#include <boost/variant.hpp>
-
 #include <plasp/utils/Parser.h>
 
 namespace plasp
diff --git a/include/plasp/pddl/expressions/Reference.h b/include/plasp/pddl/expressions/Reference.h
index 489ffd0..b41879a 100644
--- a/include/plasp/pddl/expressions/Reference.h
+++ b/include/plasp/pddl/expressions/Reference.h
@@ -1,6 +1,8 @@
 #ifndef __PLASP__PDDL__EXPRESSIONS__REFERENCE_H
 #define __PLASP__PDDL__EXPRESSIONS__REFERENCE_H
 
+#include <boost/assert.hpp>
+
 #include <plasp/pddl/Expression.h>
 #include <plasp/pddl/ExpressionVisitor.h>
 #include <plasp/utils/Parser.h>
diff --git a/include/plasp/pddl/expressions/Type.h b/include/plasp/pddl/expressions/Type.h
index fbd57f1..d7118a5 100644
--- a/include/plasp/pddl/expressions/Type.h
+++ b/include/plasp/pddl/expressions/Type.h
@@ -1,11 +1,7 @@
 #ifndef __PLASP__PDDL__EXPRESSIONS__TYPE_H
 #define __PLASP__PDDL__EXPRESSIONS__TYPE_H
 
-#include <boost/variant.hpp>
-
-#include <plasp/pddl/expressions/Either.h>
-#include <plasp/pddl/expressions/PrimitiveType.h>
-#include <plasp/utils/Parser.h>
+#include <plasp/pddl/Expression.h>
 
 namespace plasp
 {
diff --git a/src/plasp/pddl/expressions/Constant.cpp b/src/plasp/pddl/expressions/Constant.cpp
index 0384eab..6dfdee2 100644
--- a/src/plasp/pddl/expressions/Constant.cpp
+++ b/src/plasp/pddl/expressions/Constant.cpp
@@ -2,6 +2,8 @@
 
 #include <algorithm>
 
+#include <boost/assert.hpp>
+
 #include <plasp/pddl/Context.h>
 #include <plasp/pddl/ExpressionVisitor.h>
 #include <plasp/pddl/expressions/PrimitiveType.h>
diff --git a/src/plasp/pddl/expressions/PrimitiveType.cpp b/src/plasp/pddl/expressions/PrimitiveType.cpp
index 14bfae4..6cb6b12 100644
--- a/src/plasp/pddl/expressions/PrimitiveType.cpp
+++ b/src/plasp/pddl/expressions/PrimitiveType.cpp
@@ -2,6 +2,8 @@
 
 #include <algorithm>
 
+#include <boost/assert.hpp>
+
 #include <plasp/pddl/Context.h>
 #include <plasp/pddl/ExpressionVisitor.h>