diff --git a/Changelog.draft.rst b/Changelog.draft.rst
index 8b599f9..2aee8d7 100644
--- a/Changelog.draft.rst
+++ b/Changelog.draft.rst
@@ -16,6 +16,8 @@ New Features
 Changes
 -------
 
+* Give more detailed error when encountering a corrupt UID mapping file.
+
 Bug Fixes
 ---------
 
diff --git a/offlineimap/folder/UIDMaps.py b/offlineimap/folder/UIDMaps.py
index e7394b5..c77fd14 100644
--- a/offlineimap/folder/UIDMaps.py
+++ b/offlineimap/folder/UIDMaps.py
@@ -45,7 +45,11 @@ class MappingFolderMixIn:
                 line = file.readline()
                 if not len(line):
                     break
-                line = line.strip()
+                try:
+                    line = line.strip()
+                except ValueError:
+                    raise Exception("Corrupt line '%s' in UID mapping file '%s'" \
+                                        %(line, mapfilename))
                 (str1, str2) = line.split(':')
                 loc = long(str1)
                 rem = long(str2)