diff --git a/accounts/forms.py b/accounts/forms.py
index c47bc61fe..1285ae36e 100644
--- a/accounts/forms.py
+++ b/accounts/forms.py
@@ -152,13 +152,19 @@ def get_user_by_email(email):
 
 class UsernameField(forms.CharField):
     """ Username field, 3~30 characters, allows only alphanumeric chars, required by default """
+
     def __init__(self, required=True):
-        #NOTE: this allows space characters for both pre-existing usernames (OK)
-        # but also for modified new ones (not OK). It does not allow them for brand new ones (OK)
+        """Validates the username field for a form. Validation for brand new usernames must have strong validation (see Regex).
+        For profile modifications, the username validation is done in ProfileForm cleaning methods, as antique usernames can
+        contain spaces but new modified ones cannot. 
+
+        Args:
+            required (bool, optional): True for RegistrationForms, false for ProfileForms
+        """
         if required:
             validators = [RegexValidator(r'^[\w.+-]+$')]  # is the same as Django UsernameValidator except for '@' symbol
         else:
-            validators = [RegexValidator(r'^[\w .+-]+$')]  #same as the last one but with space characters included   
+            validators = []  
         super().__init__(
             label="Username",
             min_length=3,
@@ -395,10 +401,16 @@ def clean_username(self):
         if not username:
             username = self.request.user.username
 
-        # If username was not changed, consider it valid
+        # If username was not changed, consider it valid. If it has, validate it to check it does not contain space characters.
         if username.lower() == self.request.user.username.lower():
-            #self.fields["username"] = UsernameField(validation=False)
             return username
+        else:
+            validator = RegexValidator(regex=r'^[\w.+-]+$',
+                                       message="The username field must contain only letters, digits, underscores, dots, dashes and plus signs.",
+                                       code='invalid')
+            if validator(username):
+                return username 
+
 
         # Check that username is not used by another user. Note that because when the maximum number of username
         # changes is reached, the "username" field of the ProfileForm is disabled and its contents won't change.