Index: opticks-0.0.1_p20191110/extg4/CMakeLists.txt
===================================================================
--- opticks-0.0.1_p20191110.orig/extg4/CMakeLists.txt
+++ opticks-0.0.1_p20191110/extg4/CMakeLists.txt
@@ -27,6 +27,7 @@ very focussed converter classes.
 
 set(G4_VERBOSE ON)
 find_package(G4         REQUIRED MODULE)
+find_package(CLHEP      REQUIRED)
 find_package(GGeo       REQUIRED CONFIG)   
 
 # just for X4GDMLWrite
@@ -143,6 +144,7 @@ set(HEADERS
 add_library( ${name}  SHARED ${SOURCES} ${HEADERS} )
 target_link_libraries( ${name} PUBLIC 
     Opticks::G4
+    CLHEP
     Opticks::GGeo
     Opticks::OpticksXercesC
 )