diff --git a/lldb/source/Interpreter/CommandObject.cpp b/lldb/source/Interpreter/CommandObject.cpp
index 63d93a26bf84..7624e8606911 100644
--- a/lldb/source/Interpreter/CommandObject.cpp
+++ b/lldb/source/Interpreter/CommandObject.cpp
@@ -344,6 +344,10 @@ CommandObject::HandleCompletion
     StringList &matches
 )
 {
+    // Default implmentation of WantsCompletion() is !WantsRawCommandString().
+    // Subclasses who want raw command string but desire, for example,
+    // argument completion should override WantsCompletion() to return true,
+    // instead.
     if (WantsRawCommandString() && !WantsCompletion())
     {
         // FIXME: Abstract telling the completion to insert the completion character.