diff --git a/Dockerfile b/Dockerfile
index ffadcb4..4850003 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -45,8 +45,8 @@ ENV MG_FOLDER_PATH="${SOFTWARE_FOLDER}/${MG_FOLDER}"
 ENV MG_BINARY_PATH="${SOFTWARE_FOLDER}/${MG_FOLDER}/bin/mg5_aMC"
 
 #### CERN ROOT environment variables
-ENV PATH=$PATH:$ROOTSYS/bin
-ENV LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$ROOTSYS/lib
+ENV PATH=${PATH:+$PATH:}$ROOTSYS/bin
+ENV LD_LIBRARY_PATH=${LD_LIBRARY_PATH:+$LD_LIBRARY_PATH:}$ROOTSYS/lib
 
 
 ### Install MadGraph 5 Python dependencies
@@ -69,7 +69,7 @@ RUN echo "set auto_convert_model T" | python3 ${MG_BINARY_PATH}
 RUN echo "import model EWdim6-full" | python3 ${MG_BINARY_PATH}
 
 # Delphes environment variables
-ENV ROOT_INCLUDE_PATH="${ROOT_INCLUDE_PATH}:${MG_FOLDER_PATH}/Delphes/external"
+ENV ROOT_INCLUDE_PATH="${ROOT_INCLUDE_PATH:+$ROOT_INCLUDE_PATH:}${MG_FOLDER_PATH}/Delphes/external"
 
 
 #### Copy files