diff --git a/admin/include/themes.class.php b/admin/include/themes.class.php
index ad32b6f7f..82622d878 100644
--- a/admin/include/themes.class.php
+++ b/admin/include/themes.class.php
@@ -80,6 +80,20 @@ class themes
           // the theme is already active
           break;
         }
+
+        $missing_parent = $this->missing_parent_theme($theme_id);
+        if (isset($missing_parent))
+        {
+          array_push(
+            $errors, 
+            sprintf(
+              l10n('Impossible to activate this theme, the parent theme is missing: %s'),
+              $missing_parent
+              )
+            );
+          
+          break;
+        }
         
         $query = "
 INSERT INTO ".THEMES_TABLE."
@@ -168,6 +182,28 @@ DELETE
     return $errors;
   }
 
+  function missing_parent_theme($theme_id)
+  {
+    if (!isset($this->fs_themes[$theme_id]['parent']))
+    {
+      return null;
+    }
+    
+    $parent = $this->fs_themes[$theme_id]['parent'];
+      
+    if ('default' == $parent)
+    {
+      return null;
+    }
+      
+    if (!isset($this->fs_themes[$parent]))
+    {
+      return $parent;
+    }
+
+    return $this->missing_parent_theme($parent);
+  }
+
   function get_children_themes($theme_id)
   {
     $children = array();
diff --git a/admin/themes/default/template/themes_installed.tpl b/admin/themes/default/template/themes_installed.tpl
index 0a5a0cc85..4b050c51c 100644
--- a/admin/themes/default/template/themes_installed.tpl
+++ b/admin/themes/default/template/themes_installed.tpl
@@ -33,13 +33,21 @@
     <div class="themeName">{$theme.name}</div>
     <div class="themeShot"><img src="{$theme.screenshot}"></div>
     <div class="themeActions">
+
+  {if $theme.activable}
       <a href="{$activate_baseurl}{$theme.id}" title="{'Make this theme available to users'|@translate}">{'Activate'|@translate}</a>
+  {else}
+      <span title="{$theme.activate_tooltip}">{'Activate'|@translate}</span>
+  {/if}
+
       |
+
   {if $theme.deletable}
       <a href="{$delete_baseurl}{$theme.id}" onclick="return confirm('{'Are you sure?'|@translate|@escape:javascript}');" title="{'Delete this theme'|@translate}">{'Delete'|@translate}</a>
   {else}
       <span title="{$theme.delete_tooltip}">{'Delete'|@translate}</span>
   {/if}
+
     </div>
     
   </div>
diff --git a/admin/themes_installed.php b/admin/themes_installed.php
index 82efe569a..dda2ab6ed 100644
--- a/admin/themes_installed.php
+++ b/admin/themes_installed.php
@@ -89,7 +89,24 @@ foreach ($themes->fs_themes as $theme_id => $fs_theme)
   }
   else
   {
+    // is the theme "activable" ?
+    $fs_theme['activable'] = true;
+    
+    $missing_parent = $themes->missing_parent_theme($theme_id);
+    if (isset($missing_parent))
+    {
+      $fs_theme['activable'] = false;
+      
+      $fs_theme['activate_tooltip'] = sprintf(
+        l10n('Impossible to activate this theme, the parent theme is missing: %s'),
+        $missing_parent
+        );
+    }
+
+    // is the theme "deletable" ?
     $children = $themes->get_children_themes($theme_id);
+
+    $fs_theme['deletable'] = true;
     
     if (count($children) > 0)
     {
@@ -100,10 +117,6 @@ foreach ($themes->fs_themes as $theme_id => $fs_theme)
         implode(', ', $children)
         );
     }
-    else
-    {
-      $fs_theme['deletable'] = true;
-    }
     
     array_push($inactive_themes, $fs_theme);
   }