diff --git a/net/dcsctp/socket/BUILD.gn b/net/dcsctp/socket/BUILD.gn
index 69307ac6b4..e7dfc582ed 100644
--- a/net/dcsctp/socket/BUILD.gn
+++ b/net/dcsctp/socket/BUILD.gn
@@ -160,6 +160,7 @@ rtc_library("dcsctp_socket") {
     "../tx:send_queue",
   ]
   sources = [
+    "callback_deferrer.cc",
     "callback_deferrer.h",
     "dcsctp_socket.cc",
     "dcsctp_socket.h",
diff --git a/net/dcsctp/socket/callback_deferrer.cc b/net/dcsctp/socket/callback_deferrer.cc
new file mode 100644
index 0000000000..1b7fbacccb
--- /dev/null
+++ b/net/dcsctp/socket/callback_deferrer.cc
@@ -0,0 +1,142 @@
+/*
+ *  Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "net/dcsctp/socket/callback_deferrer.h"
+
+namespace dcsctp {
+namespace {
+// A wrapper around the move-only DcSctpMessage, to let it be captured in a
+// lambda.
+class MessageDeliverer {
+ public:
+  explicit MessageDeliverer(DcSctpMessage&& message)
+      : state_(rtc::make_ref_counted<State>(std::move(message))) {}
+
+  void Deliver(DcSctpSocketCallbacks& c) {
+    // Really ensure that it's only called once.
+    RTC_DCHECK(!state_->has_delivered);
+    state_->has_delivered = true;
+    c.OnMessageReceived(std::move(state_->message));
+  }
+
+ private:
+  struct State : public rtc::RefCountInterface {
+    explicit State(DcSctpMessage&& m)
+        : has_delivered(false), message(std::move(m)) {}
+    bool has_delivered;
+    DcSctpMessage message;
+  };
+  rtc::scoped_refptr<State> state_;
+};
+}  // namespace
+
+void CallbackDeferrer::TriggerDeferred() {
+  // Need to swap here. The client may call into the library from within a
+  // callback, and that might result in adding new callbacks to this instance,
+  // and the vector can't be modified while iterated on.
+  std::vector<std::function<void(DcSctpSocketCallbacks & cb)>> deferred;
+  deferred.swap(deferred_);
+
+  for (auto& cb : deferred) {
+    cb(underlying_);
+  }
+}
+
+SendPacketStatus CallbackDeferrer::SendPacketWithStatus(
+    rtc::ArrayView<const uint8_t> data) {
+  // Will not be deferred - call directly.
+  return underlying_.SendPacketWithStatus(data);
+}
+
+std::unique_ptr<Timeout> CallbackDeferrer::CreateTimeout() {
+  // Will not be deferred - call directly.
+  return underlying_.CreateTimeout();
+}
+
+TimeMs CallbackDeferrer::TimeMillis() {
+  // Will not be deferred - call directly.
+  return underlying_.TimeMillis();
+}
+
+uint32_t CallbackDeferrer::GetRandomInt(uint32_t low, uint32_t high) {
+  // Will not be deferred - call directly.
+  return underlying_.GetRandomInt(low, high);
+}
+
+void CallbackDeferrer::OnMessageReceived(DcSctpMessage message) {
+  deferred_.emplace_back(
+      [deliverer = MessageDeliverer(std::move(message))](
+          DcSctpSocketCallbacks& cb) mutable { deliverer.Deliver(cb); });
+}
+
+void CallbackDeferrer::OnError(ErrorKind error, absl::string_view message) {
+  deferred_.emplace_back(
+      [error, message = std::string(message)](DcSctpSocketCallbacks& cb) {
+        cb.OnError(error, message);
+      });
+}
+
+void CallbackDeferrer::OnAborted(ErrorKind error, absl::string_view message) {
+  deferred_.emplace_back(
+      [error, message = std::string(message)](DcSctpSocketCallbacks& cb) {
+        cb.OnAborted(error, message);
+      });
+}
+
+void CallbackDeferrer::OnConnected() {
+  deferred_.emplace_back([](DcSctpSocketCallbacks& cb) { cb.OnConnected(); });
+}
+
+void CallbackDeferrer::OnClosed() {
+  deferred_.emplace_back([](DcSctpSocketCallbacks& cb) { cb.OnClosed(); });
+}
+
+void CallbackDeferrer::OnConnectionRestarted() {
+  deferred_.emplace_back(
+      [](DcSctpSocketCallbacks& cb) { cb.OnConnectionRestarted(); });
+}
+
+void CallbackDeferrer::OnStreamsResetFailed(
+    rtc::ArrayView<const StreamID> outgoing_streams,
+    absl::string_view reason) {
+  deferred_.emplace_back(
+      [streams = std::vector<StreamID>(outgoing_streams.begin(),
+                                       outgoing_streams.end()),
+       reason = std::string(reason)](DcSctpSocketCallbacks& cb) {
+        cb.OnStreamsResetFailed(streams, reason);
+      });
+}
+
+void CallbackDeferrer::OnStreamsResetPerformed(
+    rtc::ArrayView<const StreamID> outgoing_streams) {
+  deferred_.emplace_back(
+      [streams = std::vector<StreamID>(outgoing_streams.begin(),
+                                       outgoing_streams.end())](
+          DcSctpSocketCallbacks& cb) { cb.OnStreamsResetPerformed(streams); });
+}
+
+void CallbackDeferrer::OnIncomingStreamsReset(
+    rtc::ArrayView<const StreamID> incoming_streams) {
+  deferred_.emplace_back(
+      [streams = std::vector<StreamID>(incoming_streams.begin(),
+                                       incoming_streams.end())](
+          DcSctpSocketCallbacks& cb) { cb.OnIncomingStreamsReset(streams); });
+}
+
+void CallbackDeferrer::OnBufferedAmountLow(StreamID stream_id) {
+  deferred_.emplace_back([stream_id](DcSctpSocketCallbacks& cb) {
+    cb.OnBufferedAmountLow(stream_id);
+  });
+}
+
+void CallbackDeferrer::OnTotalBufferedAmountLow() {
+  deferred_.emplace_back(
+      [](DcSctpSocketCallbacks& cb) { cb.OnTotalBufferedAmountLow(); });
+}
+}  // namespace dcsctp
diff --git a/net/dcsctp/socket/callback_deferrer.h b/net/dcsctp/socket/callback_deferrer.h
index b3251c84d5..ab2739feb1 100644
--- a/net/dcsctp/socket/callback_deferrer.h
+++ b/net/dcsctp/socket/callback_deferrer.h
@@ -47,136 +47,30 @@ class CallbackDeferrer : public DcSctpSocketCallbacks {
   explicit CallbackDeferrer(DcSctpSocketCallbacks& underlying)
       : underlying_(underlying) {}
 
-  void TriggerDeferred() {
-    // Need to swap here. The client may call into the library from within a
-    // callback, and that might result in adding new callbacks to this instance,
-    // and the vector can't be modified while iterated on.
-    std::vector<std::function<void(DcSctpSocketCallbacks & cb)>> deferred;
-    deferred.swap(deferred_);
-
-    for (auto& cb : deferred) {
-      cb(underlying_);
-    }
-  }
+  void TriggerDeferred();
 
+  // Implementation of DcSctpSocketCallbacks
   SendPacketStatus SendPacketWithStatus(
-      rtc::ArrayView<const uint8_t> data) override {
-    // Will not be deferred - call directly.
-    return underlying_.SendPacketWithStatus(data);
-  }
-
-  std::unique_ptr<Timeout> CreateTimeout() override {
-    // Will not be deferred - call directly.
-    return underlying_.CreateTimeout();
-  }
-
-  TimeMs TimeMillis() override {
-    // Will not be deferred - call directly.
-    return underlying_.TimeMillis();
-  }
-
-  uint32_t GetRandomInt(uint32_t low, uint32_t high) override {
-    // Will not be deferred - call directly.
-    return underlying_.GetRandomInt(low, high);
-  }
-
-  void OnMessageReceived(DcSctpMessage message) override {
-    deferred_.emplace_back(
-        [deliverer = MessageDeliverer(std::move(message))](
-            DcSctpSocketCallbacks& cb) mutable { deliverer.Deliver(cb); });
-  }
-
-  void OnError(ErrorKind error, absl::string_view message) override {
-    deferred_.emplace_back(
-        [error, message = std::string(message)](DcSctpSocketCallbacks& cb) {
-          cb.OnError(error, message);
-        });
-  }
-
-  void OnAborted(ErrorKind error, absl::string_view message) override {
-    deferred_.emplace_back(
-        [error, message = std::string(message)](DcSctpSocketCallbacks& cb) {
-          cb.OnAborted(error, message);
-        });
-  }
-
-  void OnConnected() override {
-    deferred_.emplace_back([](DcSctpSocketCallbacks& cb) { cb.OnConnected(); });
-  }
-
-  void OnClosed() override {
-    deferred_.emplace_back([](DcSctpSocketCallbacks& cb) { cb.OnClosed(); });
-  }
-
-  void OnConnectionRestarted() override {
-    deferred_.emplace_back(
-        [](DcSctpSocketCallbacks& cb) { cb.OnConnectionRestarted(); });
-  }
-
+      rtc::ArrayView<const uint8_t> data) override;
+  std::unique_ptr<Timeout> CreateTimeout() override;
+  TimeMs TimeMillis() override;
+  uint32_t GetRandomInt(uint32_t low, uint32_t high) override;
+  void OnMessageReceived(DcSctpMessage message) override;
+  void OnError(ErrorKind error, absl::string_view message) override;
+  void OnAborted(ErrorKind error, absl::string_view message) override;
+  void OnConnected() override;
+  void OnClosed() override;
+  void OnConnectionRestarted() override;
   void OnStreamsResetFailed(rtc::ArrayView<const StreamID> outgoing_streams,
-                            absl::string_view reason) override {
-    deferred_.emplace_back(
-        [streams = std::vector<StreamID>(outgoing_streams.begin(),
-                                         outgoing_streams.end()),
-         reason = std::string(reason)](DcSctpSocketCallbacks& cb) {
-          cb.OnStreamsResetFailed(streams, reason);
-        });
-  }
-
+                            absl::string_view reason) override;
   void OnStreamsResetPerformed(
-      rtc::ArrayView<const StreamID> outgoing_streams) override {
-    deferred_.emplace_back(
-        [streams = std::vector<StreamID>(outgoing_streams.begin(),
-                                         outgoing_streams.end())](
-            DcSctpSocketCallbacks& cb) {
-          cb.OnStreamsResetPerformed(streams);
-        });
-  }
-
+      rtc::ArrayView<const StreamID> outgoing_streams) override;
   void OnIncomingStreamsReset(
-      rtc::ArrayView<const StreamID> incoming_streams) override {
-    deferred_.emplace_back(
-        [streams = std::vector<StreamID>(incoming_streams.begin(),
-                                         incoming_streams.end())](
-            DcSctpSocketCallbacks& cb) { cb.OnIncomingStreamsReset(streams); });
-  }
-
-  void OnBufferedAmountLow(StreamID stream_id) override {
-    deferred_.emplace_back([stream_id](DcSctpSocketCallbacks& cb) {
-      cb.OnBufferedAmountLow(stream_id);
-    });
-  }
-
-  void OnTotalBufferedAmountLow() override {
-    deferred_.emplace_back(
-        [](DcSctpSocketCallbacks& cb) { cb.OnTotalBufferedAmountLow(); });
-  }
+      rtc::ArrayView<const StreamID> incoming_streams) override;
+  void OnBufferedAmountLow(StreamID stream_id) override;
+  void OnTotalBufferedAmountLow() override;
 
  private:
-  // A wrapper around the move-only DcSctpMessage, to let it be captured in a
-  // lambda.
-  class MessageDeliverer {
-   public:
-    explicit MessageDeliverer(DcSctpMessage&& message)
-        : state_(rtc::make_ref_counted<State>(std::move(message))) {}
-
-    void Deliver(DcSctpSocketCallbacks& c) {
-      // Really ensure that it's only called once.
-      RTC_DCHECK(!state_->has_delivered);
-      state_->has_delivered = true;
-      c.OnMessageReceived(std::move(state_->message));
-    }
-
-   private:
-    struct State : public rtc::RefCountInterface {
-      explicit State(DcSctpMessage&& m)
-          : has_delivered(false), message(std::move(m)) {}
-      bool has_delivered;
-      DcSctpMessage message;
-    };
-    rtc::scoped_refptr<State> state_;
-  };
-
   DcSctpSocketCallbacks& underlying_;
   std::vector<std::function<void(DcSctpSocketCallbacks& cb)>> deferred_;
 };