diff --git a/code/X3DExporter.cpp b/code/X3DExporter.cpp
index 9e89b5b9e..31a391c47 100644
--- a/code/X3DExporter.cpp
+++ b/code/X3DExporter.cpp
@@ -140,7 +140,7 @@ void X3DExporter::AttrHelper_Col3DArrToString(const aiColor3D* pArray, const siz
 	AttrHelper_CommaToPoint(pTargetString);
 }
 
-void X3DExporter::AttrHelper_Color3ToAttrList(std::list<SAttribute> pList, const std::string& pName, const aiColor3D& pValue, const aiColor3D& pDefaultValue)
+void X3DExporter::AttrHelper_Color3ToAttrList(std::list<SAttribute>& pList, const std::string& pName, const aiColor3D& pValue, const aiColor3D& pDefaultValue)
 {
 string tstr;
 
@@ -150,7 +150,7 @@ string tstr;
 	pList.push_back({pName, tstr});
 }
 
-void X3DExporter::AttrHelper_FloatToAttrList(std::list<SAttribute> pList, const string& pName, const float pValue, const float pDefaultValue)
+void X3DExporter::AttrHelper_FloatToAttrList(std::list<SAttribute>& pList, const string& pName, const float pValue, const float pDefaultValue)
 {
 string tstr;
 
diff --git a/code/X3DExporter.hpp b/code/X3DExporter.hpp
index 20aec951b..bf1e72218 100644
--- a/code/X3DExporter.hpp
+++ b/code/X3DExporter.hpp
@@ -134,7 +134,7 @@ private:
 
 	/// \fn void AttrHelper_FloatToAttrList(std::list<SAttribute> pList, const std::string& pName, const float pValue, const float pDefaultValue)
 	/// \overload void AttrHelper_Col3DArrToString(const aiColor3D* pArray, const size_t pArray_Size, std::string& pTargetString)
-	void AttrHelper_FloatToAttrList(std::list<SAttribute> pList, const std::string& pName, const float pValue, const float pDefaultValue);
+	void AttrHelper_FloatToAttrList(std::list<SAttribute> &pList, const std::string& pName, const float pValue, const float pDefaultValue);
 
 	/// \fn void AttrHelper_Color3ToAttrList(std::list<SAttribute> pList, const std::string& pName, const aiColor3D& pValue, const aiColor3D& pDefaultValue)
 	/// Add attribute to list if value not equal to default.
@@ -142,7 +142,7 @@ private:
 	/// \param [in] pName - name of new attribute.
 	/// \param [in] pValue - value of the new attribute.
 	/// \param [in] pDefaultValue - default value for checking: if pValue is equal to pDefaultValue then attribute will not be added.
-	void AttrHelper_Color3ToAttrList(std::list<SAttribute> pList, const std::string& pName, const aiColor3D& pValue, const aiColor3D& pDefaultValue);
+	void AttrHelper_Color3ToAttrList(std::list<SAttribute> &pList, const std::string& pName, const aiColor3D& pValue, const aiColor3D& pDefaultValue);
 
 	/// \fn void NodeHelper_OpenNode(const std::string& pNodeName, const size_t pTabLevel, const bool pEmptyElement, const std::list<SAttribute>& pAttrList)
 	/// Begin new XML-node element.