diff -rupN gmsh-4.0.0-source/CMakeLists.txt gmsh-4.0.0-source-new/CMakeLists.txt
--- gmsh-4.0.0-source/CMakeLists.txt	2018-08-29 10:24:05.651924683 +0200
+++ gmsh-4.0.0-source-new/CMakeLists.txt	2018-08-29 10:24:05.776924676 +0200
@@ -1748,6 +1748,8 @@ else(WIN32 OR CYGWIN)
   set(GMSH_INC ${CMAKE_INSTALL_INCLUDEDIR})
 endif(WIN32 OR CYGWIN)
 
+execute_process ( COMMAND python3 -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())" OUTPUT_VARIABLE PYTHON3_SITE_PACKAGES OUTPUT_STRIP_TRAILING_WHITESPACE)
+
 # FIXME: change this once we understand rpaths
 if(APPLE)
   if(ENABLE_BUILD_DYNAMIC OR ENABLE_BUILD_SHARED)
@@ -1769,11 +1771,11 @@ if(ENABLE_BUILD_SHARED OR ENABLE_BUILD_D
 endif(ENABLE_BUILD_SHARED OR ENABLE_BUILD_DYNAMIC)
 
 if(ENABLE_ONELAB)
-  install(FILES ${ONELAB_PY} DESTINATION ${GMSH_BIN})
+  install(FILES ${ONELAB_PY} DESTINATION ${PYTHON3_SITE_PACKAGES})
 endif(ENABLE_ONELAB)
 if(ENABLE_BUILD_LIB OR ENABLE_BUILD_SHARED OR ENABLE_BUILD_DYNAMIC)
   install(FILES ${GMSH_API} DESTINATION ${GMSH_INC})
-  install(FILES ${GMSH_PY} DESTINATION ${GMSH_LIB})
+  install(FILES ${GMSH_PY} DESTINATION ${PYTHON3_SITE_PACKAGES})
   install(FILES ${GMSH_JL} DESTINATION ${GMSH_LIB})
   if(ENABLE_PRIVATE_API)
     install(FILES ${GMSH_PRIVATE_API} DESTINATION ${GMSH_INC}/gmsh)
diff -rupN gmsh-4.0.0-source/Common/GmshMessage.cpp gmsh-4.0.0-source-new/Common/GmshMessage.cpp
--- gmsh-4.0.0-source/Common/GmshMessage.cpp	2018-06-27 22:44:49.000000000 +0200
+++ gmsh-4.0.0-source-new/Common/GmshMessage.cpp	2018-08-29 10:24:05.777924676 +0200
@@ -154,12 +154,6 @@ void Msg::Init(int argc, char **argv)
   if(CTX::instance()->exeFileName.empty() && argc && argv)
     CTX::instance()->exeFileName = argv[0];
 
-  // add the directory where the binary is installed to the path where Python
-  // looks for modules, and to the path for executables (this allows us to find
-  // the onelab.py module or subclients automatically)
-  addGmshPathToEnvironmentVar("PYTHONPATH");
-  addGmshPathToEnvironmentVar("PATH");
-
   InitializeOnelab("Gmsh");
 }