diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index d6377dbf52..36c46a81c0 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -1108,7 +1108,10 @@ class Manifest(object):
             """Convert the URL provided in :param:`href` from a reference
             relative to this manifest item to a book-absolute reference.
             """
-            purl = urlparse(href)
+            try:
+                purl = urlparse(href)
+            except ValueError:
+                return href
             scheme = purl.scheme
             if scheme and scheme != 'file':
                 return href
diff --git a/src/calibre/ebooks/oeb/polish/container.py b/src/calibre/ebooks/oeb/polish/container.py
index b38a0babe2..198cfae728 100644
--- a/src/calibre/ebooks/oeb/polish/container.py
+++ b/src/calibre/ebooks/oeb/polish/container.py
@@ -97,7 +97,10 @@ def name_to_href(name, root, base=None, quote=urlquote):
 
 def href_to_name(href, root, base=None):
     base = root if base is None else os.path.dirname(name_to_abspath(base, root))
-    purl = urlparse(href)
+    try:
+        purl = urlparse(href)
+    except ValueError:
+        return None
     if purl.scheme or not purl.path:
         return None
     href = urlunquote(purl.path)
@@ -1458,5 +1461,3 @@ def test_roundtrip():
 
 if __name__ == '__main__':
     test_roundtrip()
-
-