diff --git a/AUTHORS b/AUTHORS
index 466af3427..4c751c34e 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -160,4 +160,5 @@ suggestions:
   Jake Bell
   Florian Hollerweger
   Thomas Sullivan
+  Tim None
 
diff --git a/ChangeLog b/ChangeLog
index 461aedfd8..1ae988c2f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -54,6 +54,8 @@ Bugs
  + Fixed bug #1065, where CmdShow issued messages in incorrect situations.
  + Partially fixed #1083, which showed 'task 0 ...' when modifying a non-
    pending task (thanks to Aikido Guy).
+ + Fixed bug #1123, which caused the undo of a 'log' command to corrupt the data
+   file (thanks to Tim None).
  + No more bash completion of, for example, 'projABC:', or of 'proj:' if
    abbreviation.minimum is greater than 4.
  + Fixed bug where shadow files are not properly created when there is a missing
diff --git a/src/TDB2.cpp b/src/TDB2.cpp
index 199d32abb..c16402bd5 100644
--- a/src/TDB2.cpp
+++ b/src/TDB2.cpp
@@ -1576,26 +1576,37 @@ void TDB2::revert ()
     {
       context.debug ("TDB::undo - task found in completed.data");
 
-      // If task now belongs back in pending.data
-      if (prior.find ("status:\"pending\"")   != std::string::npos ||
-          prior.find ("status:\"waiting\"")   != std::string::npos ||
-          prior.find ("status:\"recurring\"") != std::string::npos)
+      // Either revert if there was a prior state, or remove the task.
+      if (prior != "")
       {
-        c.erase (task);
-        p.push_back (prior);
-        File::write (completed._file._data, c);
-        File::write (pending._file._data, p);
-        File::write (undo._file._data, u);
-        std::cout << STRING_TDB2_REVERTED << "\n";
-        context.debug ("TDB::undo - task belongs in pending.data");
+        *task = prior;
+        if (task->find ("status:\"pending\"")   != std::string::npos ||
+            task->find ("status:\"waiting\"")   != std::string::npos ||
+            task->find ("status:\"recurring\"") != std::string::npos)
+        {
+          c.erase (task);
+          p.push_back (prior);
+          File::write (completed._file._data, c);
+          File::write (pending._file._data, p);
+          File::write (undo._file._data, u);
+          std::cout << STRING_TDB2_REVERTED << "\n";
+          context.debug ("TDB::undo - task belongs in pending.data");
+        }
+        else
+        {
+          File::write (completed._file._data, c);
+          File::write (undo._file._data, u);
+          std::cout << STRING_TDB2_REVERTED << "\n";
+          context.debug ("TDB::undo - task belongs in completed.data");
+        }
       }
       else
       {
-        *task = prior;
+        c.erase (task);
         File::write (completed._file._data, c);
         File::write (undo._file._data, u);
         std::cout << STRING_TDB2_REVERTED << "\n";
-        context.debug ("TDB::undo - task belongs in completed.data");
+        context.debug ("TDB::undo - task removed");
       }
 
       std::cout << STRING_TDB2_UNDO_COMPLETE << "\n";