diff --git a/src/commands/CmdShorten.cpp b/src/commands/CmdShorten.cpp
index bba0a265..6a3ac36d 100644
--- a/src/commands/CmdShorten.cpp
+++ b/src/commands/CmdShorten.cpp
@@ -26,6 +26,7 @@
 
 #include <cmake.h>
 #include <Duration.h>
+#include <format.h>
 #include <commands.h>
 #include <timew.h>
 #include <iostream>
@@ -53,8 +54,6 @@ int CmdShorten (
   if (! ids.size ())
     throw std::string ("IDs must be specified. See 'timew help shorten'.");
 
-  // TODO Support :adjust
-
   // Load the data.
   // Note: There is no filter.
   Interval filter;
@@ -63,37 +62,26 @@ int CmdShorten (
   // Apply tags to ids.
   for (auto& id : ids)
   {
-    if (id <= static_cast <int> (tracked.size ()))
-    {
-      // Note: It's okay to subtract a one-based number from a zero-based index.
-      Interval i = tracked[tracked.size () - id];
-      if (! i.range.is_open ())
-      {
-        Duration dur (delta);
-        if (dur < (i.range.end - i.range.start))
-        {
-          database.deleteInterval (tracked[tracked.size () - id]);
+    if (id > static_cast <int> (tracked.size ()))
+      throw format ("ID '@{1}' does not correspond to any tracking.", id);
 
-          i.range.end -= dur.toTime_t ();
-          validate (cli, rules, database, i);
-          database.addInterval (i);
+    // Note: It's okay to subtract a one-based number from a zero-based index.
+    Interval i = tracked[tracked.size () - id];
+    if (i.range.is_open ())
+      throw format ("Cannot shorten open interval @{1}", id);
 
-          // Feedback.
-          if (rules.getBoolean ("verbose"))
-            std::cout << "Shortened @" << id << " by " << dur.formatHours () << '\n';
-        }
-        else
-          std::cout << "Cannot shorten interval @"
-                    << id
-                    << " by "
-                    << dur.formatHours ()
-                    << " because it is only "
-                    << Duration (i.range.end - i.range.start).formatHours ()
-                    << " in length.\n";
-      }
-      else
-        std::cout << "Cannot shorten open interval @" << id << '\n';
-    }
+    Duration dur (delta);
+    if (dur >= (i.range.end - i.range.start))
+      throw format ("Cannot shorten interval @{1} by {2} because it is only {3} in length.", id, dur.formatHours (), Duration (i.range.end - i.range.start).formatHours ());
+
+    database.deleteInterval (tracked[tracked.size () - id]);
+
+    i.range.end -= dur.toTime_t ();
+    validate (cli, rules, database, i);
+    database.addInterval (i);
+
+    if (rules.getBoolean ("verbose"))
+      std::cout << "Shortened @" << id << " by " << dur.formatHours () << '\n';
   }
 
   return 0;