diff --git a/xmodule/mako_block.py b/xmodule/mako_block.py
index 6e6a78910465..abf3a93f3858 100644
--- a/xmodule/mako_block.py
+++ b/xmodule/mako_block.py
@@ -17,15 +17,18 @@ def __init__(self, render_template, **kwargs):
 
         self.render_template = render_template
 
-        # Add the MakoService to the descriptor system.
+        # Add the MakoService to the runtime services.
+        # If it already exists, do not attempt to reinitialize it; otherwise, this could override the `namespace_prefix`
+        # of the `MakoService`, breaking template rendering in Studio.
         #
         # This is not needed by most XBlocks, because the MakoService is added to their runtimes.
         # However, there are a few cases where the MakoService is not added to the XBlock's
         # runtime. Specifically:
         # * in the Instructor Dashboard bulk emails tab, when rendering the HtmlBlock for its WYSIWYG editor.
         # * during testing, when fetching factory-created blocks.
-        from common.djangoapps.edxmako.services import MakoService
-        self._services['mako'] = MakoService()
+        if 'mako' not in self._services:
+            from common.djangoapps.edxmako.services import MakoService
+            self._services['mako'] = MakoService()
 
 
 class MakoTemplateBlockBase: