diff --git a/Lib/site.py b/Lib/site.py
index 868b7cb..1b4953f 100644
--- a/Lib/site.py
+++ b/Lib/site.py
@@ -515,6 +515,20 @@ def execusercustomize():
                 "'import usercustomize' failed; use -v for traceback"
 
 
+def ambiguous_python_version_rpmbuild_warn():
+    """Put a warning on stderr if /usr/bin/python is used in rpmbuild."""
+    if (sys.executable == "/usr/bin/python" and "RPM_BUILD_ROOT" in os.environ
+            and not os.environ.get("DISABLE_AMBIGUOUS_PYTHON_VERSION_WARNING")):
+        print>>sys.stderr, \
+                ("DEPRECATION WARNING: python2 invoked with /usr/bin/python.\n"
+                 "    Use /usr/bin/python3 or /usr/bin/python2\n"
+                 "    /usr/bin/python will be removed or switched to Python 3"
+                 " in the future.\n"
+                 "    If you cannot make the switch now, please follow"
+                 " instructions at "
+                 "https://fedoraproject.org/wiki/XXX#Quick_Opt-Out")
+
+
 def main():
     global ENABLE_USER_SITE
 
@@ -543,6 +557,7 @@ def main():
     # this module is run as a script, because this code is executed twice.
     if hasattr(sys, "setdefaultencoding"):
         del sys.setdefaultencoding
+    ambiguous_python_version_rpmbuild_warn()
 
 main()