diff --git a/pkgs/sagemath-categories/tox.ini b/pkgs/sagemath-categories/tox.ini
index f05668393cb..831b361256a 100644
--- a/pkgs/sagemath-categories/tox.ini
+++ b/pkgs/sagemath-categories/tox.ini
@@ -15,6 +15,10 @@ setenv =
     # Sage scripts such as sage-runtests like to use $HOME/.sage
     HOME={envdir}
 
+passenv =
+    SAGE_NUM_THREADS
+    SAGE_NUM_THREADS_PARALLEL
+
 whitelist_externals =
     bash
 
diff --git a/pkgs/sagemath-objects/setup.py b/pkgs/sagemath-objects/setup.py
index b53284f75b7..b988cbeaac1 100644
--- a/pkgs/sagemath-objects/setup.py
+++ b/pkgs/sagemath-objects/setup.py
@@ -14,19 +14,29 @@
 import sys
 sys.path.insert(0, os.path.dirname(__file__))
 
+if len(sys.argv) > 1 and (sys.argv[1] == "sdist" or sys.argv[1] == "egg_info"):
+    sdist = True
+else:
+    sdist = False
+
 import sage.env
 sage.env.default_required_modules = sage.env.default_optional_modules = ()
 
 from sage_setup.command.sage_build_cython import sage_build_cython
 from sage_setup.command.sage_build_ext import sage_build_ext
 
-from sage_setup.find import find_python_sources
-python_packages, python_modules, cython_modules = find_python_sources(
-    '.', ['sage'])   # for now, we do the filtering using MANIFEST
-
-log.warn('python_packages = {0}'.format(python_packages))
-log.warn('python_modules = {0}'.format(python_modules))
-log.warn('cython_modules = {0}'.format(cython_modules))
+if sdist:
+    python_packages = []
+    python_modules = []
+    cython_modules = []
+else:
+    from sage_setup.find import find_python_sources
+    python_packages, python_modules, cython_modules = find_python_sources(
+        '.', ['sage'])   # for now, we do the filtering using MANIFEST
+
+    log.warn('python_packages = {0}'.format(python_packages))
+    log.warn('python_modules = {0}'.format(python_modules))
+    log.warn('cython_modules = {0}'.format(cython_modules))
 
 setup(
     cmdclass = dict(build_cython=sage_build_cython,
diff --git a/pkgs/sagemath-objects/tox.ini b/pkgs/sagemath-objects/tox.ini
index d676cb7d8f5..a1244f7aa8c 100644
--- a/pkgs/sagemath-objects/tox.ini
+++ b/pkgs/sagemath-objects/tox.ini
@@ -15,6 +15,10 @@ setenv =
     # Sage scripts such as sage-runtests like to use $HOME/.sage
     HOME={envdir}
 
+passenv =
+    SAGE_NUM_THREADS
+    SAGE_NUM_THREADS_PARALLEL
+
 whitelist_externals =
     bash