diff --git a/accounts/forms.py b/accounts/forms.py
index ed4f32923..8a5cf7817 100644
--- a/accounts/forms.py
+++ b/accounts/forms.py
@@ -152,12 +152,24 @@ 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):
+        """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.+-]+$')]  # is the same as Django UsernameValidator except for '@' symbol
+        else:
+            validators = []  
         super().__init__(
             label="Username",
             min_length=3,
             max_length=30,
-            validators=[RegexValidator(r'^[\w.+-]+$')],  # is the same as Django UsernameValidator except for '@' symbol
+            validators=validators,
             help_text="30 characters or fewer. Can contain: letters, digits, underscores, dots, dashes and plus signs.",
             error_messages={'invalid': "The username field must contain only letters, digits, underscores, dots, dashes and "
                                        "plus signs."},
@@ -389,9 +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():
             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.
diff --git a/accounts/tests/test_user.py b/accounts/tests/test_user.py
index 7c682ad45..3be72b7f3 100644
--- a/accounts/tests/test_user.py
+++ b/accounts/tests/test_user.py
@@ -1085,7 +1085,30 @@ def test_oldusername_username_unique_case_insensitiveness(self):
         OldUsername.objects.create(user=userA, username='newUserAUsername')
         with self.assertRaises(IntegrityError):
             OldUsername.objects.create(user=userA, username='NewUserAUsername')
+    
+    def test_username_whitespace(self):
+        """Test that for usernames created before stronger validation was applied, whitespaces are a valid character
+        but for new edited ones they are not."""
+        userA = User.objects.create_user('user A', email='userA@freesound.org', password='testpass')
+        self.client.force_login(userA)
+
+        # Test save profile without changing username with whitespaces
+        resp = self.client.post(reverse('accounts-edit'), data={'profile-username': ['user A'], 'profile-ui_theme_preference': 'f'})
+        self.assertRedirects(resp, reverse('accounts-edit'))
+        self.assertEqual(OldUsername.objects.filter(user=userA).count(), 0)
 
+        # Test save profile changing username (no whitespaces)
+        resp = self.client.post(reverse('accounts-edit'), data={'profile-username': ['userANewName'], 'profile-ui_theme_preference': 'f'})
+        self.assertRedirects(resp, reverse('accounts-edit'))
+        userA.refresh_from_db()
+        self.assertEqual(OldUsername.objects.filter(user=userA).count(), 1)
+
+        # Test save profile changing username (whitespaces -> fail)
+        resp = self.client.post(reverse('accounts-edit'), data={'profile-username': ['userA SpaceName'], 'profile-ui_theme_preference': 'f'})
+        self.assertEqual(resp.status_code, 200)
+        userA.refresh_from_db()
+        self.assertEqual(userA.username, 'userANewName')
+        self.assertEqual(OldUsername.objects.filter(user=userA).count(), 1)
 
 class ChangeEmailViaAdminTestCase(TestCase):