diff --git a/PROBLEMS b/PROBLEMS
index e36e9b694..4a04a74bb 100644
--- a/PROBLEMS
+++ b/PROBLEMS
@@ -35,10 +35,6 @@
   poll() calls to be without timeout. Or something similar, depending
   on case.
 
-- Recursive mutexes are evil. The last remaining instances should be
-  removed from the Kit/ChildSession.cppp as/when we move to a single
-  threaded Kit process.
-
 - Occasionally Control-C (SIGINT) doesn't shut down coolwsd. One has
   to kill it with SIGKILL. Which of course leaves all the chroot jails
   around. Hitting Control-C a second time will attempt a faster, and
diff --git a/common/SigUtil.cpp b/common/SigUtil.cpp
index 64334cab7..f47930bea 100644
--- a/common/SigUtil.cpp
+++ b/common/SigUtil.cpp
@@ -29,7 +29,6 @@
 #include <fstream>
 #include <iomanip>
 #include <iostream>
-#include <mutex>
 #include <sstream>
 #include <string>
 #include <thread>
diff --git a/net/DelaySocket.cpp b/net/DelaySocket.cpp
index f4a338929..757863a2d 100644
--- a/net/DelaySocket.cpp
+++ b/net/DelaySocket.cpp
@@ -10,7 +10,6 @@
 #include <net/DelaySocket.hpp>
 
 #include <memory>
-#include <mutex>
 
 #define DELAY_LOG(X) std::cerr << X << '\n';
 
diff --git a/net/DelaySocket.hpp b/net/DelaySocket.hpp
index 256433f87..1ea83b64b 100644
--- a/net/DelaySocket.hpp
+++ b/net/DelaySocket.hpp
@@ -9,8 +9,6 @@
 
 #include <Socket.hpp>
 
-#include <mutex>
-
 /// Simulates network latency for local debugging.
 ///
 /// We are lifecycle managed internally based on the physical /
diff --git a/wsd/Admin.cpp b/wsd/Admin.cpp
index 0a27540e4..9c9154db3 100644
--- a/wsd/Admin.cpp
+++ b/wsd/Admin.cpp
@@ -9,7 +9,6 @@
 #include <config.h>
 
 #include <cassert>
-#include <mutex>
 #include <sys/poll.h>
 #include <unistd.h>
 
diff --git a/wsd/Admin.hpp b/wsd/Admin.hpp
index 546f62e0d..c1bdefb4c 100644
--- a/wsd/Admin.hpp
+++ b/wsd/Admin.hpp
@@ -7,8 +7,6 @@
 
 #pragma once
 
-#include <mutex>
-
 #include "AdminModel.hpp"
 #include "Log.hpp"