diff --git a/src/calibre/srv/http.py b/src/calibre/srv/http.py
index a2e50658cb..7f90ae55f8 100644
--- a/src/calibre/srv/http.py
+++ b/src/calibre/srv/http.py
@@ -586,6 +586,10 @@ class HTTPPair(object):
                 if not self.close_connection:
                     self.outheaders.set('Connection', 'Keep-Alive')
 
+        ct = self.outheaders.get('Content-Type', '')
+        if ct.startswith('text/') and 'charset=' not in ct:
+            self.outheaders.set('Content-Type', ct + '; charset=UTF-8')
+
         buf = [HTTP11 + (' %d ' % self.status_code) + httplib.responses[self.status_code]]
         for header, value in sorted(self.outheaders.iteritems(), key=itemgetter(0)):
             buf.append('%s: %s' % (header, value))
diff --git a/src/calibre/srv/respond.py b/src/calibre/srv/respond.py
index 9c16879d3f..d48ea94e9a 100644
--- a/src/calibre/srv/respond.py
+++ b/src/calibre/srv/respond.py
@@ -210,10 +210,9 @@ class DynamicOutput(object):
             self.data = output
         else:
             self.data = output.encode('utf-8')
-            ct = outheaders.get('Content-Type', 'text/plain')
-            if 'charset=' not in ct:
-                ct += '; charset=UTF-8'
-            outheaders.set('Content-Type', ct, replace_all=True)
+            ct = outheaders.get('Content-Type')
+            if not ct:
+                outheaders.set('Content-Type', 'text/plain; charset=UTF-8', replace_all=True)
         self.content_length = len(self.data)
         self.etag = None
         self.accept_ranges = False