diff --git a/weblab/entities/forms.py b/weblab/entities/forms.py
index 2ef48547a..6c0bd49b2 100644
--- a/weblab/entities/forms.py
+++ b/weblab/entities/forms.py
@@ -1,6 +1,7 @@
 from braces.forms import UserKwargModelFormMixin
 from django import forms
 from django.core.exceptions import ValidationError
+from django.core.validators import RegexValidator
 from django.forms import formset_factory
 
 from accounts.models import User
@@ -57,7 +58,9 @@ class EntityVersionForm(forms.Form):
     )
     tag = forms.CharField(
         help_text='Optional short label for this version',
-        required=False)
+        required=False,
+        validators=[RegexValidator(r'[-_A-Za-z0-9]', 'Please enter a valid tag name. '
+                                                     'Only letters, numbers, dashes or underscores are allowed.' )])
     commit_message = forms.CharField(
         label='Description of this version',
         widget=forms.Textarea)
@@ -94,7 +97,9 @@ class EntityTagVersionForm(forms.Form):
     tag = forms.CharField(
         label='New tag',
         help_text='Short label for this version',
-        required=True)
+        required=True,
+        validators=[RegexValidator(r'[-_A-Za-z0-9]', 'Please enter a valid tag name.'
+                                                     ' Only letters, numbers, dashes or underscores are allowed.')])
 
 
 class EntityCollaboratorForm(forms.Form):