diff --git a/Installation/include/CGAL/config.h b/Installation/include/CGAL/config.h
index 69797f4b536..9421212b20a 100644
--- a/Installation/include/CGAL/config.h
+++ b/Installation/include/CGAL/config.h
@@ -30,6 +30,11 @@
 #ifndef CGAL_CONFIG_H
 #define CGAL_CONFIG_H
 
+// CGAL is header-only by default since CGAL-5.0.
+#if !defined(CGAL_HEADER_ONLY) && ! CGAL_NOT_HEADER_ONLY
+#  define CGAL_HEADER_ONLY 1
+#endif
+
 #ifdef CGAL_HEADER_ONLY
 #  define CGAL_NO_AUTOLINK 1
 #endif
@@ -152,9 +157,6 @@
 //  platform specific workaround flags (CGAL_CFG_...)
 //----------------------------------------------------------------------//
 
-#if ! CGAL_NOT_HEADER_ONLY
-#  define CGAL_HEADER_ONLY 1
-#endif
 #if CGAL_HEADER_ONLY
 #  include <CGAL/internal/enable_third_party_libraries.h>
 #  if(BOOST_MSVC)