diff --git a/src/assets/init.js b/src/assets/init.js
index b48385c..5b1575a 100644
--- a/src/assets/init.js
+++ b/src/assets/init.js
@@ -35,7 +35,7 @@ var createIframe = function() {
 }
 
 var load_virtual_page = (function (path, get_params, anchor) {
-    const data = window.global_context.file_tree[path];
+    const data = window.global_context.file_tree[path].data;
     var iframe = createIframe();
     window.global_context.get_parameters = get_params;
     iframe.contentDocument.write(data);
diff --git a/src/assets/inject.js b/src/assets/inject.js
index 07a2e5a..8cb2b34 100644
--- a/src/assets/inject.js
+++ b/src/assets/inject.js
@@ -142,7 +142,7 @@ var is_virtual = function(url) {
 var retrieve_file = function(path) {
     // console.log("Retrieving file: " + path);
     var file_tree = window.global_context.file_tree;
-    var file = file_tree[path];
+    var file = file_tree[path].data;
     return file;
 };
 
diff --git a/src/embed.py b/src/embed.py
index 09d0244..8b5cafb 100644
--- a/src/embed.py
+++ b/src/embed.py
@@ -107,6 +107,7 @@ def prepare_file(filename, before, after):
     _, ext = os.path.splitext(filename)
     ext = ext.lower()[1:]
     data = open(filename, 'rb').read()
+    mime_type = mime_type_from_bytes(data)
 
     if ext == 'css':
         # assuming all CSS files have names ending in '.css'
@@ -134,7 +135,12 @@ def prepare_file(filename, before, after):
 
     logger.debug('loaded file: %s [%d]' % (filename, len(data)))
 
-    return data
+    result = {
+        'data': data,
+        'mime_type': mime_type,
+    }
+
+    return result
 
 
 def deflate(data):
@@ -217,9 +223,7 @@ def embed_css_resources(css, filename):
             mime_type = 'text/css'
             content = embed_css_resources(content, filename)
         else:
-            from io import BytesIO
-            from sphinx.util.images import guess_mimetype_for_stream
-            mime_type = guess_mimetype_for_stream(BytesIO(content))
+            mime_type = mime_type_from_bytes(content)
         if not mime_type:
             logger.error('Unable to determine mime type: %s' % path)
             mime_type = 'application/octet-stream'
@@ -237,6 +241,13 @@ def embed_css_resources(css, filename):
     return css
 
 
+def mime_type_from_bytes(buffer):
+    from io import BytesIO
+    from sphinx.util.images import guess_mimetype_for_stream
+    mime_type = guess_mimetype_for_stream(BytesIO(buffer))
+    return mime_type
+
+
 def load_filetree(base_dir, before=None, after=None, exclude_pattern=None):
     """Load entire directory in a dict"""