diff --git a/ipynbsrv/core/models.py b/ipynbsrv/core/models.py
index bd959b3..ade260d 100644
--- a/ipynbsrv/core/models.py
+++ b/ipynbsrv/core/models.py
@@ -776,7 +776,7 @@ class ContainerImage(models.Model):
         max_length=75,
         validators=[
             RegexValidator(
-                regex='^[A-z][\w\/]*$',
+                regex='^[A-z][\w\/-]*$',
                 message='Invalid container snapshot name.'
             )
         ]
diff --git a/ipynbsrv/web/templates/web/container_snapshots/modal_create.html b/ipynbsrv/web/templates/web/container_snapshots/modal_create.html
index b87aa5e..d6647b2 100644
--- a/ipynbsrv/web/templates/web/container_snapshots/modal_create.html
+++ b/ipynbsrv/web/templates/web/container_snapshots/modal_create.html
@@ -13,8 +13,8 @@ <h4 class="modal-title">New Container Snapshot</h4>
                     <input name="ct_id" type="hidden" class="form-control" value="{{ container.id }}">
                     <div class="form-group">
                         <label for="name">Name</label>
-                        <input name="name" type="text" pattern="[A-Za-z1-9_-]+" class="form-control" required>
-                        <p class="help-text">Allowed pattern: ^[A-z]\w*$</p>
+                        <input name="name" type="text" pattern="^[A-z]\w*$" class="form-control" required>
+                        <p class="help-block">Allowed pattern: ^[A-z]\w*$</p>
                     </div>
                     <div class="form-group">
                         <label for="description">Description</label>
diff --git a/ipynbsrv/web/templates/web/containers/modal_create.html b/ipynbsrv/web/templates/web/containers/modal_create.html
index 0eb0299..73940bc 100644
--- a/ipynbsrv/web/templates/web/containers/modal_create.html
+++ b/ipynbsrv/web/templates/web/containers/modal_create.html
@@ -12,7 +12,8 @@ <h4 class="modal-title">New container</h4>
                  <div class="modal-body">
                     <div class="form-group">
                         <label for="name">Name</label>
-                        <input name="name" type="text" pattern="[A-Za-z1-9_-]+" class="form-control" placeholder="e.g IPython Notebook" required>
+                        <input name="name" type="text" pattern="^[A-z]\w*$" class="form-control" placeholder="e.g IPython Notebook" required>
+                        <p class="help-block">Allowed pattern: ^[A-z]\w*$</p>
                     </div>
                     <div class="form-group">
                         <label for="description">Description</label>
diff --git a/ipynbsrv/web/templates/web/images/modal_create.html b/ipynbsrv/web/templates/web/images/modal_create.html
index 3ba0380..2e0b5e9 100644
--- a/ipynbsrv/web/templates/web/images/modal_create.html
+++ b/ipynbsrv/web/templates/web/images/modal_create.html
@@ -23,8 +23,8 @@ <h4 class="modal-title">New image</h4>
                     </div>
                     <div class="form-group">
                         <label for="img_name">Name</label>
-                        <input name="img_name" type="text" pattern="[A-Za-z1-9_-]+" class="form-control" placeholder="e.g fhnw-maths " required>
-                        <p class="help-text">Allowed pattern: ^[A-z][\w\/]*$</p>
+                        <input name="img_name" type="text" pattern="^[A-z][\w\/]*$" class="form-control" placeholder="e.g fhnw-maths " required>
+                        <p class="help-block">Allowed pattern: ^[A-z][\w\/]*$</p>
                     </div>
                     <div class="form-group">
                         <label for="description">Description</label>