diff --git a/Installation/cmake/modules/CGAL_Macros.cmake b/Installation/cmake/modules/CGAL_Macros.cmake
index 7ab86320278..099e3f133e8 100644
--- a/Installation/cmake/modules/CGAL_Macros.cmake
+++ b/Installation/cmake/modules/CGAL_Macros.cmake
@@ -208,7 +208,7 @@ if( NOT CGAL_MACROS_FILE_INCLUDED )
 
     set (vlib ${CGAL_EXT_LIB_${lib}_PREFIX} )
 
-    if ( ${vlib}_FOUND )
+    if ( WITH_${lib} AND ${vlib}_FOUND )
 
       if ( NOT ${vlib}_SETUP ) # avoid double usage
   
@@ -222,6 +222,7 @@ if( NOT CGAL_MACROS_FILE_INCLUDED )
           message (STATUS "Configured ${lib} from UseLIB-file: ${filename}")
 
           # UseLIB-file has to set ${vlib}_SETUP to TRUE
+          # TODO EBEB what about Qt4, Qt3, zlib?
 
         else()
 
@@ -253,7 +254,9 @@ if( NOT CGAL_MACROS_FILE_INCLUDED )
 
     else()
 
-      message( FATAL_ERROR "Try to use ${lib} that is not found")
+      if ( WITH_${lib} )
+        message( SEND_ERROR "Try to use ${lib} that is not found")
+      endif()
 
     endif()
 
diff --git a/Installation/cmake/modules/CGAL_SetupDependencies.cmake b/Installation/cmake/modules/CGAL_SetupDependencies.cmake
index ee59161a576..4187bf3e50e 100644
--- a/Installation/cmake/modules/CGAL_SetupDependencies.cmake
+++ b/Installation/cmake/modules/CGAL_SetupDependencies.cmake
@@ -9,11 +9,12 @@ foreach (lib ${CGAL_SUPPORTING_3RD_PARTY_LIRARIES})
   set (vlib "${CGAL_EXT_LIB_${lib}_PREFIX}")
 
   list(FIND CGAL_MANDATORY_3RD_PARTY_LIBRARIES "${lib}" POSITION)
-  if ("${POSITION}" STRGREATER "-1" OR WITH_${lib})
-   
+  #if ("${POSITION}" STRGREATER "-1" OR WITH_${lib})
+  if (WITH_${lib}) 
+
     # message (STATUS "With ${lib} given")
 
-    message (STATUS "Checking expected library: ${lib} ...")
+    message (STATUS "Preconfiguring library: ${lib} ...")
     
     find_package( ${lib} )
    
@@ -24,7 +25,8 @@ foreach (lib ${CGAL_SUPPORTING_3RD_PARTY_LIRARIES})
       message( STATUS "  ${lib} libraries:    ${${vlib}_LIBRARIES}" )
       message( STATUS "  ${lib} definitions:  ${${vlib}_DEFINITIONS}" )
    
-      set ( CGAL_USE_${vlib} TRUE )
+      # TODO EBEB delete CGAL_USE_${vlib} TRUE here as set in "use_lib" macro, what about Qt3, Qt4, zlib etc?
+      ### set ( CGAL_USE_${vlib} TRUE )
 
       # Part 2: Add some lib-specific definitions or obtain version
    
@@ -62,6 +64,10 @@ foreach (lib ${CGAL_SUPPORTING_3RD_PARTY_LIRARIES})
 
 endforeach()
 
+if( (GMP_FOUND AND NOT MPFR_FOUND) OR (NOT GMP_FOUND AND MPFR_FOUND) )
+  message( FATAL_ERROR "CGAL needs for its full functionality both GMP and MPFR.")
+endif()
+
 if( NOT GMP_FOUND )
   set(CGAL_NO_CORE ON)
   message( STATUS "CGAL_Core needs GMP, cannot be configured.")
diff --git a/Installation/cmake/modules/FindGMPXX.cmake b/Installation/cmake/modules/FindGMPXX.cmake
index 333cd1d44b6..e24a62316fa 100644
--- a/Installation/cmake/modules/FindGMPXX.cmake
+++ b/Installation/cmake/modules/FindGMPXX.cmake
@@ -9,7 +9,7 @@
 
 find_package( GMP QUIET )
 
-if(GMP_FOUND)
+if(WITH_GMP AND GMP_FOUND)
 
   if (GMPXX_INCLUDE_DIR AND GMPXX_LIBRARIES)
     # Already in cache, be silent
@@ -30,4 +30,8 @@ if(GMP_FOUND)
   
   find_package_handle_standard_args(GMPXX "DEFAULT_MSG" GMPXX_LIBRARIES GMPXX_INCLUDE_DIR )
 
+else()
+
+  message( FATAL_ERROR "GMPXX needs GMP")
+
 endif()
diff --git a/Installation/cmake/modules/FindNTL.cmake b/Installation/cmake/modules/FindNTL.cmake
index 594a37d3dd0..32c89b87102 100644
--- a/Installation/cmake/modules/FindNTL.cmake
+++ b/Installation/cmake/modules/FindNTL.cmake
@@ -3,12 +3,12 @@
 
 find_package( GMP REQUIRED )
 
-if( NOT GMP_FOUND )
+if( NOT WITH_GMP OR NOT GMP_FOUND )
 
   message( FATAL_ERROR "NTL requires GMP" )
   set( NTL_FOUND FALSE )
 
-else( NOT GMP_FOUND )
+else( NOT WITH_GMP OR NOT GMP_FOUND )
 
   include( CGAL_VersionUtils )
 
@@ -96,7 +96,7 @@ else( NOT GMP_FOUND )
 
   endif( _IS_GMP_VERSION_TOO_LOW )
 
-endif( NOT GMP_FOUND )
+endif( NOT WITH_GMP OR NOT GMP_FOUND )
 
 if ( NTL_FOUND )
 #  if ( NOT NTL_FIND_QUIETLY )