A new SCons release, 4.5.1, is now available on the SCons download page: https://scons.org/pages/download.html Here is a summary of the changes since 4.5.0: FIXES ----- - Fix a problem in 4.5.0 where using something like the following code will cause a Clone()'d environment to share the CPPDEFINES with the original Environment() which was cloned. Causing leakage of changes to CPPDEFINES when they should be completely independent after the Clone. env=Environment(CPPDEFINES=['a']) env.Append(CPPDEFINES=['b']) (or AppendUnique,Prepend,PrependUnique) env1=env.Clone() env1.Append(CPPDEFINES=['c']) (or any other modification, but not overwriting CPPDEFINES) Now env['CPPDEFINES'] will contain 'c' when it should not. Thanks to the following contributors listed below for their contributions to this release. ========================================================================================== .. code-block:: text git shortlog --no-merges -ns 4.5.0..HEAD 3 William Deegan 1 Mats Wichmann