diff --git a/gui/CLASSWin.cxx b/gui/CLASSWin.cxx
index 9f3cf2a629b6e550dcc2889770d05f89a18366cc..e00d8bf2183a5845383f585d9ce47be4fe939bd0 100644
--- a/gui/CLASSWin.cxx
+++ b/gui/CLASSWin.cxx
@@ -15,7 +15,7 @@
 #include <TGTableLayout.h>
 #include <TGResourcePool.h>
 #include <TLine.h>
-#include "external/StringLine.hxx"
+#include "StringLine.hxx"
 
 // For all class not defined in file.hxx see http://root.cern.ch/root/html/
 // For example : for TGraphErrors see http://root.cern.ch/root/html/TGraphErrors.html
diff --git a/gui/CMakeLists.txt b/gui/CMakeLists.txt
index b3fa09a62138a5a2f0c03cf2253b38f66e065b49..4f4ba41f417c804b94b7cd344f17b04718858ea5 100644
--- a/gui/CMakeLists.txt
+++ b/gui/CMakeLists.txt
@@ -1,4 +1,5 @@
-INCLUDE_DIRECTORIES( ${CLASS_HEADERS_DIR_INCLUDE} )
+INCLUDE_DIRECTORIES(${CLASS_HEADERS_DIR_INCLUDE} ${CLASS_HEADERS_DIR_EXTERNAL})
+
 add_executable (CLASSgui CLASSGui.cxx CLASSPlotElement.cxx CLASSWin.cxx CLASSRead.cxx)
 target_link_libraries(CLASSgui CLASSpkg)
 
diff --git a/source/Model/Equivalence/CMakeLists.txt b/source/Model/Equivalence/CMakeLists.txt
index 2be1b6026f6a22d6507255fcc74c603a6024aa14..0d37dde2384a9c9cdd2c134231b7d39d8dbcd5a4 100644
--- a/source/Model/Equivalence/CMakeLists.txt
+++ b/source/Model/Equivalence/CMakeLists.txt
@@ -3,4 +3,4 @@
 # ----------------------------------------------------------
 
 # include directories 
-SET( CLASS_HEADERS_DIR_EQUIVALENCE ${CMAKE_CURRENT_SOURCE_DIR} PARENT_SCOPE)
+SET( CLASS_HEADERS_DIR_EQUIVALENCE ${CMAKE_CURRENT_SOURCE_DIR}  CACHE INTERNAL "")
diff --git a/source/Model/Irradiation/CMakeLists.txt b/source/Model/Irradiation/CMakeLists.txt
index 46f0e6cffba5586d55beb09e6425b3770283436f..2e6c25b4b12297f05d61eead52f71248688d024e 100644
--- a/source/Model/Irradiation/CMakeLists.txt
+++ b/source/Model/Irradiation/CMakeLists.txt
@@ -3,4 +3,4 @@
 # ----------------------------------------------------------
 
 # include directories 
-SET( CLASS_HEADERS_DIR_IRRADIATION ${CMAKE_CURRENT_SOURCE_DIR} PARENT_SCOPE)
+SET( CLASS_HEADERS_DIR_IRRADIATION ${CMAKE_CURRENT_SOURCE_DIR}  CACHE INTERNAL "")
diff --git a/source/Model/XS/CMakeLists.txt b/source/Model/XS/CMakeLists.txt
index bf4b41485245fff77a7ed4fdbdc31badf9fa7692..d6805649f7324d6e6d11042674b0ec9dd39372a2 100644
--- a/source/Model/XS/CMakeLists.txt
+++ b/source/Model/XS/CMakeLists.txt
@@ -3,5 +3,5 @@
 # ----------------------------------------------------------
 
 # include directories 
-SET( CLASS_HEADERS_DIR_XS ${CMAKE_CURRENT_SOURCE_DIR} PARENT_SCOPE)
+SET( CLASS_HEADERS_DIR_XS ${CMAKE_CURRENT_SOURCE_DIR}  CACHE INTERNAL "")
 
diff --git a/source/external/CMakeLists.txt b/source/external/CMakeLists.txt
index 9746f57492145ea24e863436b810a508dc99d4b6..f4cc50e004adbec0a767aa1ee9ea1d02658604fe 100644
--- a/source/external/CMakeLists.txt
+++ b/source/external/CMakeLists.txt
@@ -3,4 +3,4 @@
 # ----------------------------------------------------------
 
 # include directories 
-SET( CLASS_HEADERS_DIR_EXTERNAL ${CMAKE_CURRENT_SOURCE_DIR} PARENT_SCOPE)
+SET( CLASS_HEADERS_DIR_EXTERNAL ${CMAKE_CURRENT_SOURCE_DIR}  CACHE INTERNAL "")