diff -up src/sage/env.py.orig src/sage/env.py
--- src/sage/env.py.orig	2020-07-06 16:57:04.139002833 -0600
+++ src/sage/env.py	2020-07-06 16:59:20.179973650 -0600
@@ -167,9 +167,9 @@ var('SAGE_SPKG_INST',      join(SAGE_LOC
 var('SAGE_LIB',            os.path.dirname(os.path.dirname(sage.__file__)))
 var('SAGE_EXTCODE',        join(SAGE_LIB, 'sage', 'ext_data'))
 
-var('SAGE_ROOT')           # no fallback for SAGE_ROOT
+var('SAGE_ROOT',           '@@SAGE_ROOT@@')
 var('SAGE_SRC',            join(SAGE_ROOT, 'src'), SAGE_LIB)
-var('SAGE_DOC_SRC',        join(SAGE_ROOT, 'src', 'doc'), SAGE_DOC)
+var('SAGE_DOC_SRC',        '@@SAGE_DOC@@')
 var('SAGE_PKGS',           join(SAGE_ROOT, 'build', 'pkgs'))
 var('SAGE_ROOT_GIT',       join(SAGE_ROOT, '.git'))