diff --git a/README.md b/README.md
index 959f025..15f65d7 100644
--- a/README.md
+++ b/README.md
@@ -66,18 +66,18 @@ xs | Size of column on extra small screens (less than 768px) | optional | 1-12 |
 sm | Size of column on small screens (greater than 768px) | optional | 1-12 | false
 md | Size of column on medium screens (greater than 992px) | optional | 1-12 | false
 lg | Size of column on large screens (greater than 1200px) | optional | 1-12 | false
-offset-xs | Offset on extra small screens | optional | 1-12 | false
-offset-sm | Offset on small screens | optional | 1-12 | false
-offset-md | Offset on column on medium screens | optional | 1-12 | false
-offset-lg | Offset on column on large screens | optional | 1-12 | false
-pull-xs | Pull on extra small screens | optional | 1-12 | false
-pull-sm | Pull on small screens | optional | 1-12 | false
-pull-md | Pull on column on medium screens | optional | 1-12 | false
-pull-lg | Pull on column on large screens | optional | 1-12 | false
-push-xs | Push on extra small screens | optional | 1-12 | false
-push-sm | Push on small screens | optional | 1-12 | false
-push-md | Push on column on medium screens | optional | 1-12 | false
-push-lg | Push on column on large screens | optional | 1-12 | false
+offset_xs | Offset on extra small screens | optional | 1-12 | false
+offset_sm | Offset on small screens | optional | 1-12 | false
+offset_md | Offset on column on medium screens | optional | 1-12 | false
+offset_lg | Offset on column on large screens | optional | 1-12 | false
+pull_xs | Pull on extra small screens | optional | 1-12 | false
+pull_sm | Pull on small screens | optional | 1-12 | false
+pull_md | Pull on column on medium screens | optional | 1-12 | false
+pull_lg | Pull on column on large screens | optional | 1-12 | false
+push_xs | Push on extra small screens | optional | 1-12 | false
+push_sm | Push on small screens | optional | 1-12 | false
+push_md | Push on column on medium screens | optional | 1-12 | false
+push_lg | Push on column on large screens | optional | 1-12 | false
 
 [Bootstrap grid documentation](http://getbootstrap.com/css/#grid).
 
diff --git a/bootstrap-shortcodes.php b/bootstrap-shortcodes.php
index e835133..300d9f4 100644
--- a/bootstrap-shortcodes.php
+++ b/bootstrap-shortcodes.php
@@ -265,36 +265,36 @@ function bs_column( $atts, $content = null ) {
       "md" => false,
       "sm" => false,
       "xs" => false,
-      "offset-lg" => false,
-      "offset-md" => false,
-      "offset-sm" => false,
-      "offset-xs" => false,
-      "pull-lg" => false,
-      "pull-md" => false,
-      "pull-sm" => false,
-      "pull-xs" => false,
-      "push-lg" => false,
-      "push-md" => false,
-      "push-sm" => false,
-      "push-xs" => false,
+      "offset_lg" => false,
+      "offset_md" => false,
+      "offset_sm" => false,
+      "offset_xs" => false,
+      "pull_lg" => false,
+      "pull_md" => false,
+      "pull_sm" => false,
+      "pull_xs" => false,
+      "push_lg" => false,
+      "push_md" => false,
+      "push_sm" => false,
+      "push_xs" => false,
     ), $atts));
     $return  =  '<div class="';
     $return .= ($lg) ? 'col-lg-' . $lg . ' ' : '';
     $return .= ($md) ? 'col-md-' . $md . ' ' : '';
     $return .= ($sm) ? 'col-sm-' . $sm . ' ' : '';
     $return .= ($xs) ? 'col-xs-' . $xs . ' ' : '';
-    $return .= ($offset-lg) ? 'col-lg-offset-' . $offset-lg . ' ' : '';
-    $return .= ($offset-md) ? 'col-md-offset-' . $offset-md . ' ' : '';
-    $return .= ($offset-sm) ? 'col-sm-offset-' . $offset-sm . ' ' : '';
-    $return .= ($offset-xs) ? 'col-xs-offset-' . $offset-xs . ' ' : '';
-    $return .= ($pull-lg) ? 'col-lg-pull-' . $pull-lg . ' ' : '';
-    $return .= ($pull-md) ? 'col-md-pull-' . $pull-md . ' ' : '';
-    $return .= ($pull-sm) ? 'col-sm-pull-' . $pull-sm . ' ' : '';
-    $return .= ($pull-xs) ? 'col-xs-pull-' . $pull-xs . ' ' : '';
-    $return .= ($push-lg) ? 'col-lg-push-' . $push-lg . ' ' : '';
-    $return .= ($push-md) ? 'col-md-push-' . $push-md . ' ' : '';
-    $return .= ($push-sm) ? 'col-sm-push-' . $push-sm . ' ' : '';
-    $return .= ($push-xs) ? 'col-xs-push-' . $push-xs . ' ' : '';
+    $return .= ($offset_lg) ? 'col-lg-offset-' . $offset_lg . ' ' : '';
+    $return .= ($offset_md) ? 'col-md-offset-' . $offset_md . ' ' : '';
+    $return .= ($offset_sm) ? 'col-sm-offset-' . $offset_sm . ' ' : '';
+    $return .= ($offset_xs) ? 'col-xs-offset-' . $offset_xs . ' ' : '';
+    $return .= ($pull_lg) ? 'col-lg-pull-' . $pull_lg . ' ' : '';
+    $return .= ($pull_md) ? 'col-md-pull-' . $pull_md . ' ' : '';
+    $return .= ($pull_sm) ? 'col-sm-pull-' . $pull_sm . ' ' : '';
+    $return .= ($pull_xs) ? 'col-xs-pull-' . $pull_xs . ' ' : '';
+    $return .= ($push_lg) ? 'col-lg-push-' . $push_lg . ' ' : '';
+    $return .= ($push_md) ? 'col-md-push-' . $push_md . ' ' : '';
+    $return .= ($push_sm) ? 'col-sm-push-' . $push_sm . ' ' : '';
+    $return .= ($push_xs) ? 'col-xs-push-' . $push_xs . ' ' : '';
     $return .= '">' . do_shortcode( $content ) . '</div>';
 
     return $return;