diff --git a/backend/app/schemas/auth.py b/backend/app/schemas/auth.py
index 41de744..ccfcf74 100644
--- a/backend/app/schemas/auth.py
+++ b/backend/app/schemas/auth.py
@@ -26,8 +26,8 @@ def _validate_username(v: str) -> str:
     v = v.strip().lower()
     if not 3 <= len(v) <= 50:
         raise ValueError("Username must be 3–50 characters")
-    if not re.fullmatch(r"[a-z0-9_\-]+", v):
-        raise ValueError("Username may only contain letters, numbers, _ and -")
+    if not re.fullmatch(r"[a-z0-9_.\-]+", v):
+        raise ValueError("Username may only contain letters, numbers, _ . and -")
     return v