diff --git a/src/zope/testrunner/find.py b/src/zope/testrunner/find.py
index cbbdedd..6a3718b 100644
--- a/src/zope/testrunner/find.py
+++ b/src/zope/testrunner/find.py
@@ -171,13 +171,8 @@ def find_tests(options, found_suites=None):
 
 
 def find_suites(options):
-    # Sort prefixes so that longest prefixes come first.
-    # That is because only first match is evaluated which
-    # can be a problem with nested source packages.
-    sorted_prefixes = [x for x in options.prefix]
-    sorted_prefixes.sort(key=lambda prefix: len(prefix[0]), reverse=True)
     for fpath, package in find_test_files(options):
-        for (prefix, prefix_package) in sorted_prefixes:
+        for (prefix, prefix_package) in options.prefix:
             if fpath.startswith(prefix) and package == prefix_package:
                 # strip prefix, strip .py suffix and convert separator to dots
                 noprefix = fpath[len(prefix):]
diff --git a/src/zope/testrunner/options.py b/src/zope/testrunner/options.py
index cab11be..07db865 100644
--- a/src/zope/testrunner/options.py
+++ b/src/zope/testrunner/options.py
@@ -624,6 +624,12 @@ def apply_auto_progress(args):
 
     options.prefix = [(path + os.path.sep, package)
                       for (path, package) in options.test_path]
+
+    # Sort prefixes so that longest prefixes come first.
+    # That is because only first match is evaluated which
+    # can be a problem with nested source packages.
+    options.prefix.sort(key=lambda p: len(p[0]), reverse=True)
+
     if options.all:
         options.at_level = sys.maxsize