Index: lldb/trunk/packages/Python/lldbsuite/test/functionalities/wrong_commands/.categories
===================================================================
--- lldb/trunk/packages/Python/lldbsuite/test/functionalities/wrong_commands/.categories
+++ lldb/trunk/packages/Python/lldbsuite/test/functionalities/wrong_commands/.categories
@@ -0,0 +1 @@
+cmdline
Index: lldb/trunk/packages/Python/lldbsuite/test/functionalities/wrong_commands/TestWrongCommands.py
===================================================================
--- lldb/trunk/packages/Python/lldbsuite/test/functionalities/wrong_commands/TestWrongCommands.py
+++ lldb/trunk/packages/Python/lldbsuite/test/functionalities/wrong_commands/TestWrongCommands.py
@@ -0,0 +1,39 @@
+"""
+Test how lldb reacts to wrong commands
+"""
+
+from __future__ import print_function
+
+import os
+import time
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class UnknownCommandTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @no_debug_info_test
+    def test_ambiguous_command(self):
+        command_interpreter = self.dbg.GetCommandInterpreter()
+        self.assertTrue(command_interpreter, VALID_COMMAND_INTERPRETER)
+        result = lldb.SBCommandReturnObject()
+
+        command_interpreter.HandleCommand("g", result)
+        self.assertFalse(result.Succeeded())
+        self.assertRegexpMatches(result.GetError(), "Ambiguous command 'g'. Possible matches:")
+        self.assertRegexpMatches(result.GetError(), "gui")
+        self.assertRegexpMatches(result.GetError(), "gdb-remote")
+        # FIXME: Somehow we get 'gui' and 'gdb-remote' twice in the output.
+
+    @no_debug_info_test
+    def test_unknown_command(self):
+        command_interpreter = self.dbg.GetCommandInterpreter()
+        self.assertTrue(command_interpreter, VALID_COMMAND_INTERPRETER)
+        result = lldb.SBCommandReturnObject()
+
+        command_interpreter.HandleCommand("qbert", result)
+        self.assertFalse(result.Succeeded())
+        self.assertEquals(result.GetError(), "error: 'qbert' is not a valid command.\n")
Index: lldb/trunk/source/Interpreter/CommandInterpreter.cpp
===================================================================
--- lldb/trunk/source/Interpreter/CommandInterpreter.cpp
+++ lldb/trunk/source/Interpreter/CommandInterpreter.cpp
@@ -1693,33 +1693,6 @@
           remainder.c_str());
 
     cmd_obj->Execute(remainder.c_str(), result);
-  } else {
-    // We didn't find the first command object, so complete the first argument.
-    Args command_args(command_string);
-    StringList matches;
-    unsigned cursor_char_position = strlen(command_args.GetArgumentAtIndex(0));
-    CompletionRequest request(command_line, cursor_char_position, 0, -1,
-                              matches);
-    int num_matches = HandleCompletionMatches(request);
-
-    if (num_matches > 0) {
-      std::string error_msg;
-      error_msg.assign("ambiguous command '");
-      error_msg.append(command_args.GetArgumentAtIndex(0));
-      error_msg.append("'.");
-
-      error_msg.append(" Possible completions:");
-      for (int i = 0; i < num_matches; i++) {
-        error_msg.append("\n\t");
-        error_msg.append(matches.GetStringAtIndex(i));
-      }
-      error_msg.append("\n");
-      result.AppendRawError(error_msg.c_str());
-    } else
-      result.AppendErrorWithFormat("Unrecognized command '%s'.\n",
-                                   command_args.GetArgumentAtIndex(0));
-
-    result.SetStatus(eReturnStatusFailed);
   }
 
   if (log)