diff --git a/base/allocator/virtual_memory_win.cc b/base/allocator/virtual_memory_win.cc
index 67bd08a2..cc6b096b 100644
--- a/base/allocator/virtual_memory_win.cc
+++ b/base/allocator/virtual_memory_win.cc
@@ -1,7 +1,7 @@
 // Copyright (C) 2022 Vincent Hengel.
 // For licensing information see LICENSE at the root of this distribution.
 
-#include <Windows.h>
+#include <windows.h>
 #include <base/allocator/virtual_memory.h>
 
 namespace base {
diff --git a/base/debugging/debugging_win.cc b/base/debugging/debugging_win.cc
index 71270e05..7b1b9f94 100644
--- a/base/debugging/debugging_win.cc
+++ b/base/debugging/debugging_win.cc
@@ -4,7 +4,7 @@
 #include "debugging.h"
 
 #if defined(OS_WIN)
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 namespace base {
diff --git a/base/dynamic_library_win.cc b/base/dynamic_library_win.cc
index 7b7b17c3..503dfddc 100644
--- a/base/dynamic_library_win.cc
+++ b/base/dynamic_library_win.cc
@@ -1,7 +1,7 @@
 // Copyright (C) 2022 Vincent Hengel.
 // For licensing information see LICENSE at the root of this distribution.
 
-#include <Windows.h>
+#include <windows.h>
 #include <base/check.h>
 #include <base/filesystem/path.h>
 #include <base/dynamic_library.h>
diff --git a/base/environment_variables_win.cc b/base/environment_variables_win.cc
index a150d558..37068111 100644
--- a/base/environment_variables_win.cc
+++ b/base/environment_variables_win.cc
@@ -1,7 +1,7 @@
 // Copyright (C) 2022 Vincent Hengel.
 // For licensing information see LICENSE at the root of this distribution.
 
-#include <Windows.h>
+#include <windows.h>
 #include <base/environment_variables.h>
 #include <base/text/code_convert.h>
 
diff --git a/base/process/process_win.cc b/base/process/process_win.cc
index b87b171b..2baa68e2 100644
--- a/base/process/process_win.cc
+++ b/base/process/process_win.cc
@@ -1,7 +1,7 @@
 // Copyright (C) 2022 Vincent Hengel.
 // For licensing information see LICENSE at the root of this distribution.
 
-#include <Windows.h>
+#include <windows.h>
 #include <base/filesystem/path.h>
 #include <base/text/code_convert.h>
 
diff --git a/base/profiling/profiler_communication.cc b/base/profiling/profiler_communication.cc
index 51ec023a..c085a15c 100644
--- a/base/profiling/profiler_communication.cc
+++ b/base/profiling/profiler_communication.cc
@@ -7,7 +7,7 @@
 #include <base/environment_variables.h>
 
 #if defined(OS_WIN)
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 #include <base/profiling/profiler_communication.h>
diff --git a/base/random/random_win.cc b/base/random/random_win.cc
index c62425d9..3b233556 100644
--- a/base/random/random_win.cc
+++ b/base/random/random_win.cc
@@ -3,8 +3,8 @@
 
 #include "random.h"
 
-#include <Windows.h>
-#include <Wincrypt.h>
+#include <windows.h>
+#include <wincrypt.h>
 
 namespace base {
 
diff --git a/base/threading/thread_win.cc b/base/threading/thread_win.cc
index 309f67c6..f7095e22 100644
--- a/base/threading/thread_win.cc
+++ b/base/threading/thread_win.cc
@@ -1,7 +1,7 @@
 // Copyright (C) Force67 <github.com/Force67>.
 // For licensing information see LICENSE at the root of this distribution.
 
-#include <Windows.h>
+#include <windows.h>
 #include <base/feature.h>
 #include <base/check.h>
 #include <base/threading/thread.h>
diff --git a/base/win/com_helpers.h b/base/win/com_helpers.h
index 3de75f1b..24b7b3f5 100644
--- a/base/win/com_helpers.h
+++ b/base/win/com_helpers.h
@@ -2,7 +2,7 @@
 // For licensing information see LICENSE at the root of this distribution.
 #pragma once
 
-#include <Shlwapi.h>
+#include <shlwapi.h>
 
 namespace base::win {
 
diff --git a/base/win/minwin.h b/base/win/minwin.h
index 82723a99..213be7d3 100644
--- a/base/win/minwin.h
+++ b/base/win/minwin.h
@@ -16,6 +16,12 @@
 #include <sal.h>
 #include <specstrings.h>
 
+#if defined(__MINGW32__)
+// __int64 is an MSVC keyword. MinGW's runtime header is what defines it there,
+// and nothing else pulled in above reaches it.
+#include <_mingw.h>
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -362,6 +368,9 @@ WINBASEAPI DWORD WINAPI WaitForSingleObject(HANDLE hHandle,
 
 WINBASEAPI BOOL WINAPI CloseHandle(HANDLE hObject);
 
+// Needed for thread_pool.cc.
+WINBASEAPI VOID WINAPI Sleep(DWORD dwMilliseconds);
+
 #ifdef __cplusplus
 }
 
diff --git a/base/win/registry_key_win.cc b/base/win/registry_key_win.cc
index 52a85b66..73463c00 100644
--- a/base/win/registry_key_win.cc
+++ b/base/win/registry_key_win.cc
@@ -3,7 +3,7 @@
 
 #include "registry_key.h"
 
-#include <Windows.h>
+#include <windows.h>
 #include <base/check.h>
 
 extern "C" __declspec(dllimport) DWORD WINAPI ExpandEnvironmentStringsW(LPCWSTR lpSrc,
diff --git a/base/win/scoped_handle.cc b/base/win/scoped_handle.cc
index a7a9ac13..41e326ba 100644
--- a/base/win/scoped_handle.cc
+++ b/base/win/scoped_handle.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <Windows.h>
+#include <windows.h>
 #include "base/win/scoped_handle.h"
 
 namespace base {