diff --git a/src/sort.cpp b/src/sort.cpp
index 3ee64f503..f99ada61c 100644
--- a/src/sort.cpp
+++ b/src/sort.cpp
@@ -30,7 +30,6 @@
 #include <string>
 #include <stdlib.h>
 #include <Context.h>
-#include <Variant.h>
 #include <ISO8601.h>
 #include <Task.h>
 #include <text.h>
@@ -68,7 +67,6 @@ void sort_tasks (
 // require re-parsing.
 //
 // Essentially a static implementation of a dynamic operator<.
-// UDA string values delegate to Variant::operator<.
 static bool sort_compare (int left, int right)
 {
   std::string field;
@@ -213,20 +211,36 @@ static bool sort_compare (int left, int right)
         return ascending ? (left_real < right_real)
                          : (left_real > right_real);
       }
-      // UDA values of type 'string' are sorted by Variant::operator<.
-      // By setting 'source' to the UDA name, the comparison operator can use
-      // the custom sort order, if defined.
       else if (type == "string")
       {
-        Variant l ((*global_data)[left].get_ref  (field));
-        Variant r ((*global_data)[right].get_ref (field));
-        if (l == r)
+        const std::string left_string = (*global_data)[left].get_ref (field);
+        const std::string right_string = (*global_data)[right].get_ref (field);
+
+        if (left_string == right_string)
           continue;
 
-        l.source (field);
-        r.source (field);
-        return ascending ? (l < r) : (r < l);
+        // UDAs of the type string can have custom sort orders, which need to be considered.
+        auto order = Task::customOrder.find (field);
+        if (order != Task::customOrder.end ())
+        {
+          // Guaranteed to be found, because of ColUDA::validate ().
+          auto posLeft  = std::find (order->second.begin (), order->second.end (), left_string);
+          auto posRight = std::find (order->second.begin (), order->second.end (), right_string);
+          return ascending ? (posLeft < posRight) : (posLeft > posRight);
+        }
+        else
+        {
+          // Empty values are unconditionally last, if no custom order was specified.
+          if (left_string == "")
+            return false;
+          else if (right_string == "")
+            return true;
+
+          return ascending ? (left_string < right_string)
+                           : (left_string > right_string);
+        }
       }
+
       else if (type == "date")
       {
         const std::string& left_string  = (*global_data)[left].get_ref  (field);