diff --git a/MaterialLib/MPL/PropertyType.cpp b/MaterialLib/MPL/PropertyType.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..64e39af3a8917d2dc698bbcc9eb4c09d20acb403
--- /dev/null
+++ b/MaterialLib/MPL/PropertyType.cpp
@@ -0,0 +1,33 @@
+/**
+ * \file
+ * \copyright
+ * Copyright (c) 2012-2021, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ */
+
+#include "PropertyType.h"
+
+#include <boost/algorithm/string/predicate.hpp>
+
+#include "BaseLib/Error.h"
+
+namespace MaterialPropertyLib
+{
+PropertyType convertStringToProperty(std::string const& string)
+{
+    for (int i = 0; i < static_cast<int>(PropertyType::number_of_properties);
+         ++i)
+    {
+        if (boost::iequals(string, property_enum_to_string[i]))
+        {
+            return static_cast<PropertyType>(i);
+        }
+    }
+
+    OGS_FATAL(
+        "The property name '{:s}' does not correspond to any known property",
+        string);
+}
+}  // namespace MaterialPropertyLib
diff --git a/MaterialLib/MPL/PropertyType.h b/MaterialLib/MPL/PropertyType.h
index 6d8744ac2863b9f64d0a88402da747fbfdc37352..4976baa9373999f579c89255aae36506a8c65d15 100644
--- a/MaterialLib/MPL/PropertyType.h
+++ b/MaterialLib/MPL/PropertyType.h
@@ -13,12 +13,9 @@
 #pragma once
 
 #include <array>
-#include <boost/algorithm/string/predicate.hpp>
 #include <memory>
 #include <string>
 
-#include "BaseLib/Error.h"
-
 namespace MaterialPropertyLib
 {
 class Property;
@@ -167,21 +164,7 @@ static const std::array<std::string, PropertyType::number_of_properties>
 
 /// This function converts a string (e.g. a string from the configuration-tree)
 /// into one of the entries of the PropertyType enumerator.
-inline PropertyType convertStringToProperty(std::string const& string)
-{
-    for (int i = 0; i < static_cast<int>(PropertyType::number_of_properties);
-         ++i)
-    {
-        if (boost::iequals(string, property_enum_to_string[i]))
-        {
-            return static_cast<PropertyType>(i);
-        }
-    }
-
-    OGS_FATAL(
-        "The property name '{:s}' does not correspond to any known property",
-        string);
-}
+PropertyType convertStringToProperty(std::string const& string);
 
 /// This data type is based on a std::array. It can hold pointers to objects of
 /// class Property or its inheritors. The size of this array is determined by