diff --git a/src/postorius/forms.py b/src/postorius/forms.py
index 7c6fb45..27babde 100644
--- a/src/postorius/forms.py
+++ b/src/postorius/forms.py
@@ -599,6 +599,7 @@
     )
     subject_prefix = forms.CharField(
         label=_('Subject prefix'),
+        strip=False,
     )