diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/multiword-commands/TestMultiWordCommands.py b/lldb/packages/Python/lldbsuite/test/functionalities/multiword-commands/TestMultiWordCommands.py
index 12d572586c40..80b144f58d57 100644
--- a/lldb/packages/Python/lldbsuite/test/functionalities/multiword-commands/TestMultiWordCommands.py
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/multiword-commands/TestMultiWordCommands.py
@@ -20,8 +20,7 @@ class MultiwordCommandsTestCase(TestBase):
 
     @no_debug_info_test
     def test_empty_subcommand(self):
-        # FIXME: This has no error message.
-        self.expect("platform \"\"", error=True)
+        self.expect("platform \"\"", error=True, substrs=["Need to specify a non-empty subcommand."])
 
     @no_debug_info_test
     def test_help(self):
diff --git a/lldb/source/Commands/CommandObjectMultiword.cpp b/lldb/source/Commands/CommandObjectMultiword.cpp
index c0f5d6703f8e..03a3770d8df7 100644
--- a/lldb/source/Commands/CommandObjectMultiword.cpp
+++ b/lldb/source/Commands/CommandObjectMultiword.cpp
@@ -94,8 +94,10 @@ bool CommandObjectMultiword::Execute(const char *args_string,
   }
 
   auto sub_command = args[0].ref();
-  if (sub_command.empty())
+  if (sub_command.empty()) {
+    result.AppendError("Need to specify a non-empty subcommand.");
     return result.Succeeded();
+  }
 
   if (sub_command.equals_lower("help")) {
     this->CommandObject::GenerateHelpText(result);