diff --git a/src/calibre/ebooks/css_transform_rules.py b/src/calibre/ebooks/css_transform_rules.py
index 8b129a5cb2..712e1253ed 100644
--- a/src/calibre/ebooks/css_transform_rules.py
+++ b/src/calibre/ebooks/css_transform_rules.py
@@ -378,7 +378,7 @@ def test(return_tests=False):  # {{{
         r = Rule(**rule)
         decl = StyleDeclaration(safe_parser().parseStyle(style))
         r.process_declaration(decl)
-        return str(decl)
+        return str(decl).rstrip(';')
 
     class TestTransforms(unittest.TestCase):
         longMessage = True
diff --git a/src/calibre/ebooks/oeb/normalize_css.py b/src/calibre/ebooks/oeb/normalize_css.py
index d5cb2eb9b2..941d000b6c 100644
--- a/src/calibre/ebooks/oeb/normalize_css.py
+++ b/src/calibre/ebooks/oeb/normalize_css.py
@@ -416,7 +416,7 @@ def test_normalization(return_tests=False):  # {{{
             css = '; '.join(f'border-{edge}-{p}: {v}' for edge in ('top',) for p, v in zip(BORDER_PROPS, vals.split()))
             style = parseStyle(css)
             condense_rule(style)
-            self.assertEqual(css_text(style), 'border-top: %s' % vals)
+            self.assertEqual(css_text(style).rstrip(';'), 'border-top: %s' % vals)
             css += ';' + '; '.join(f'border-{edge}-{p}: {v}' for edge in ('right', 'left', 'bottom') for p, v in
                              zip(BORDER_PROPS, vals.replace('red', 'green').split()))
             style = parseStyle(css)
diff --git a/src/calibre/ebooks/oeb/polish/tests/cascade.py b/src/calibre/ebooks/oeb/polish/tests/cascade.py
index aa7ca98cfa..5372bd9c79 100644
--- a/src/calibre/ebooks/oeb/polish/tests/cascade.py
+++ b/src/calibre/ebooks/oeb/polish/tests/cascade.py
@@ -212,7 +212,7 @@ class CascadeTest(BaseTest):
         style = parseStyle('background-image: url(b.png); background: black url(a.png) fixed')
         for prop in style.getProperties(all=True):
             remove_property_value(prop, lambda val:'png' in val.cssText)
-        self.assertEqual('background: black fixed', style.cssText)
+        self.assertEqual('background: black fixed', style.cssText.rstrip(';'))
 
     def test_fallback_font_matching(self):
         def cf(id, weight='normal', style='normal', stretch='normal'):
diff --git a/src/calibre/utils/run_tests.py b/src/calibre/utils/run_tests.py
index 27145d91e3..9468453029 100644
--- a/src/calibre/utils/run_tests.py
+++ b/src/calibre/utils/run_tests.py
@@ -84,8 +84,10 @@ def itertests(suite):
 def init_env():
     from calibre.utils.config_base import reset_tweaks_to_default
     from calibre.ebooks.metadata.book.base import reset_field_metadata
+    from calibre.ebooks.oeb.polish.utils import setup_css_parser_serialization
     reset_tweaks_to_default()
     reset_field_metadata()
+    setup_css_parser_serialization()
 
 
 def filter_tests(suite, test_ok):