diff --git a/libtransmission/announcer-http.cc b/libtransmission/announcer-http.cc
index f2d1b2927..3c664b9c3 100644
--- a/libtransmission/announcer-http.cc
+++ b/libtransmission/announcer-http.cc
@@ -4,6 +4,7 @@
 // License text can be found in the licenses/ folder.
 
 #include <algorithm> // std::copy_n()
+#include <cctype>
 #include <cstdio> /* fprintf() */
 #include <iomanip>
 #include <iostream>
diff --git a/libtransmission/bandwidth.h b/libtransmission/bandwidth.h
index 2b6525f7f..cbac8cc4b 100644
--- a/libtransmission/bandwidth.h
+++ b/libtransmission/bandwidth.h
@@ -13,6 +13,7 @@
 #include <cstddef> // size_t
 #include <cstdint> // uint64_t
 #include <memory>
+#include <utility> // for std::move()
 #include <vector>
 
 #include "transmission.h"
diff --git a/libtransmission/file-posix.cc b/libtransmission/file-posix.cc
index 68fafb239..97307fac2 100644
--- a/libtransmission/file-posix.cc
+++ b/libtransmission/file-posix.cc
@@ -12,7 +12,6 @@
 #include <climits> /* PATH_MAX */
 #include <cstdint> /* SIZE_MAX */
 #include <cstdio>
-#include <cstring>
 #include <string_view>
 #include <string>
 #include <vector>
diff --git a/libtransmission/file-win32.cc b/libtransmission/file-win32.cc
index 8d5d8f17a..490f0e417 100644
--- a/libtransmission/file-win32.cc
+++ b/libtransmission/file-win32.cc
@@ -6,6 +6,7 @@
 #include <algorithm>
 #include <array>
 #include <cctype> // for isalpha()
+#include <cstring>
 #include <iterator> // for std::back_inserter
 #include <string>
 #include <string_view>
diff --git a/libtransmission/handshake.cc b/libtransmission/handshake.cc
index 43f1c4d67..a79c1f4af 100644
--- a/libtransmission/handshake.cc
+++ b/libtransmission/handshake.cc
@@ -6,7 +6,6 @@
 #include <algorithm>
 #include <array>
 #include <cerrno>
-#include <chrono>
 #include <string_view>
 #include <utility>
 
diff --git a/libtransmission/log.cc b/libtransmission/log.cc
index ae6a677a6..9c65df1b2 100644
--- a/libtransmission/log.cc
+++ b/libtransmission/log.cc
@@ -5,6 +5,7 @@
 
 #include <array>
 #include <cerrno>
+#include <chrono>
 #include <cstdio>
 #include <map>
 #include <mutex>
diff --git a/libtransmission/peer-msgs.cc b/libtransmission/peer-msgs.cc
index 1a3ffb1a5..62f129d3c 100644
--- a/libtransmission/peer-msgs.cc
+++ b/libtransmission/peer-msgs.cc
@@ -6,7 +6,6 @@
 #include <algorithm>
 #include <array>
 #include <cerrno>
-#include <chrono>
 #include <cstring>
 #include <ctime>
 #include <iterator>
diff --git a/libtransmission/rpc-server.cc b/libtransmission/rpc-server.cc
index edcd515a5..06306fca9 100644
--- a/libtransmission/rpc-server.cc
+++ b/libtransmission/rpc-server.cc
@@ -6,7 +6,7 @@
 #include <algorithm>
 #include <array>
 #include <chrono>
-#include <cstring> /* memcpy */
+#include <cstring> /* for strcspn() */
 #include <ctime>
 #include <memory>
 #include <string>
diff --git a/libtransmission/torrent-files.cc b/libtransmission/torrent-files.cc
index 4d57be3ef..92f402734 100644
--- a/libtransmission/torrent-files.cc
+++ b/libtransmission/torrent-files.cc
@@ -4,6 +4,7 @@
 // License text can be found in the licenses/ folder.
 
 #include <algorithm> // std::find()
+#include <cctype>
 #include <functional>
 #include <iterator>
 #include <optional>
diff --git a/libtransmission/torrent-metainfo.cc b/libtransmission/torrent-metainfo.cc
index 48226b6b8..74eb60706 100644
--- a/libtransmission/torrent-metainfo.cc
+++ b/libtransmission/torrent-metainfo.cc
@@ -5,7 +5,6 @@
 
 #include <algorithm>
 #include <array>
-#include <cctype>
 #include <cerrno> // for EINVAL
 #include <string>
 #include <string_view>
diff --git a/libtransmission/transmission.h b/libtransmission/transmission.h
index c8d46672f..d4fcf10e2 100644
--- a/libtransmission/transmission.h
+++ b/libtransmission/transmission.h
@@ -1,16 +1,10 @@
-/*
- * This file Copyright © Transmission authors and contributors.
- *
- * It may be used under the 3-Clause BSD License, the GNU Public License v2,
- * or v3, or any future license endorsed by Mnemosyne LLC.
- *
- */
+// This file Copyright © Transmission authors and contributors.
+// It may be used under the 3-Clause BSD (SPDX: BSD-3-Clause),
+// GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
+// or any future license endorsed by Mnemosyne LLC.
+// License text can be found in the licenses/ folder.
 
-/*
- * This file defines the public API for the libtransmission library.
- * The other public API headers are variant.h and utils.h.
- * Most of the remaining headers in libtransmission are private.
- */
+// This file defines the public API for the libtransmission library.
 
 #pragma once
 
diff --git a/libtransmission/trevent.cc b/libtransmission/trevent.cc
index d214bd9bc..1271ea760 100644
--- a/libtransmission/trevent.cc
+++ b/libtransmission/trevent.cc
@@ -3,6 +3,7 @@
 // or any future license endorsed by Mnemosyne LLC.
 // License text can be found in the licenses/ folder.
 
+#include <chrono>
 #include <condition_variable>
 #include <functional>
 #include <list>
diff --git a/libtransmission/upnp.cc b/libtransmission/upnp.cc
index 5ad4a05d7..c6df4f339 100644
--- a/libtransmission/upnp.cc
+++ b/libtransmission/upnp.cc
@@ -5,6 +5,7 @@
 
 #include <array>
 #include <cerrno>
+#include <chrono>
 #include <future>
 #include <mutex>
 #include <string>
diff --git a/libtransmission/utils.cc b/libtransmission/utils.cc
index 3a5a31eed..0fa55abc9 100644
--- a/libtransmission/utils.cc
+++ b/libtransmission/utils.cc
@@ -5,6 +5,7 @@
 
 #include <algorithm> // for std::sort, std::transform
 #include <array> // std::array
+#include <cctype>
 #include <cerrno>
 #include <cfloat> // DBL_DIG
 #include <chrono>
diff --git a/libtransmission/variant.cc b/libtransmission/variant.cc
index 2bc5f7525..0633b5b23 100644
--- a/libtransmission/variant.cc
+++ b/libtransmission/variant.cc
@@ -8,6 +8,7 @@
 #include <stack>
 #include <string>
 #include <string_view>
+#include <utility>
 #include <vector>
 
 #ifdef _WIN32
diff --git a/libtransmission/watchdir.cc b/libtransmission/watchdir.cc
index 393936906..cebcad7c6 100644
--- a/libtransmission/watchdir.cc
+++ b/libtransmission/watchdir.cc
@@ -5,6 +5,7 @@
 
 #define LIBTRANSMISSION_WATCHDIR_MODULE
 
+#include <chrono>
 #include <set>
 
 #include "transmission.h"
diff --git a/libtransmission/watchdir.h b/libtransmission/watchdir.h
index afadc5c4e..0b86c2af2 100644
--- a/libtransmission/watchdir.h
+++ b/libtransmission/watchdir.h
@@ -5,6 +5,7 @@
 
 #pragma once
 
+#include <chrono>
 #include <functional>
 #include <memory>
 #include <string_view>
diff --git a/libtransmission/webseed.cc b/libtransmission/webseed.cc
index bf10efce6..acb506223 100644
--- a/libtransmission/webseed.cc
+++ b/libtransmission/webseed.cc
@@ -4,7 +4,6 @@
 // License text can be found in the licenses/ folder.
 
 #include <algorithm>
-#include <chrono>
 #include <iterator>
 #include <memory>
 #include <numeric> // std::accumulate()
diff --git a/qt/Session.cc b/qt/Session.cc
index 3d1950578..98f090bda 100644
--- a/qt/Session.cc
+++ b/qt/Session.cc
@@ -7,6 +7,7 @@
 #include <array>
 #include <cassert>
 #include <string_view>
+#include <utility>
 
 #include <QApplication>
 #include <QByteArray>