diff --git a/rtc_base/cancer_stick_castle.h b/rtc_base/cancer_stick_castle.h
index 43e6a46a70..df142c26cb 100644
--- a/rtc_base/cancer_stick_castle.h
+++ b/rtc_base/cancer_stick_castle.h
@@ -24,13 +24,20 @@ namespace cancer_stick_castle_impl {
 class CancerStickCastleReceivers {
  public:
   CancerStickCastleReceivers();
+  CancerStickCastleReceivers(const CancerStickCastleReceivers&) = delete;
+  CancerStickCastleReceivers& operator=(const CancerStickCastleReceivers&) =
+      delete;
+  CancerStickCastleReceivers(CancerStickCastleReceivers&&) = delete;
+  CancerStickCastleReceivers& operator=(CancerStickCastleReceivers&&) = delete;
   ~CancerStickCastleReceivers();
+
   void AddReceiver(UntypedFunction&& f) {
     AddReceiverImpl(&f);
     // Assume that f was moved from and is now trivially destructible.
     // This helps the compiler optimize away the destructor call.
     RTC_ASSUME(f.IsTriviallyDestructible());
   }
+
   void Foreach(rtc::FunctionView<void(UntypedFunction&)> fv);
 
  private:
@@ -43,6 +50,8 @@ class CancerStickCastleReceivers {
 // A collection of receivers (callable objects) that can be called all at once.
 // Optimized for minimal binary size.
 //
+// Neither copyable nor movable. Could easily be made movable if necessary.
+//
 // TODO(kwiberg): Add support for removing receivers, if necessary. AddReceiver
 // would have to return some sort of ID that the caller could save and then pass
 // to RemoveReceiver. Alternatively, the callable objects could return one value
@@ -51,11 +60,22 @@ class CancerStickCastleReceivers {
 template <typename... ArgT>
 class CancerStickCastle {
  public:
+  CancerStickCastle() = default;
+  CancerStickCastle(const CancerStickCastle&) = delete;
+  CancerStickCastle& operator=(const CancerStickCastle&) = delete;
+  CancerStickCastle(CancerStickCastle&&) = delete;
+  CancerStickCastle& operator=(CancerStickCastle&&) = delete;
+
+  // Adds a new receiver. The receiver (a callable object or a function pointer)
+  // must be movable, but need not be copyable. Its call signature should be
+  // `void(ArgT...)`.
   template <typename F>
   void AddReceiver(F&& f) {
     receivers_.AddReceiver(
         UntypedFunction::Create<void(ArgT...)>(std::forward<F>(f)));
   }
+
+  // Calls all receivers with the given arguments.
   void Send(ArgT&&... args) {
     receivers_.Foreach([&](UntypedFunction& f) {
       f.Call<void(ArgT...)>(std::forward<ArgT>(args)...);