diff --git a/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5nodeinstanceclientproxy.cpp b/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5nodeinstanceclientproxy.cpp
index 1e8828f6849..44eaab88d22 100644
--- a/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5nodeinstanceclientproxy.cpp
+++ b/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5nodeinstanceclientproxy.cpp
@@ -41,7 +41,7 @@
 #if defined(Q_OS_UNIX)
 #include <unistd.h>
 #elif defined(Q_OS_WIN)
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 namespace QmlDesigner {
diff --git a/share/qtcreator/qml/qmlpuppet/qml2puppet/qml2puppetmain.cpp b/share/qtcreator/qml/qmlpuppet/qml2puppet/qml2puppetmain.cpp
index 51b265a593b..4b3d047142e 100644
--- a/share/qtcreator/qml/qmlpuppet/qml2puppet/qml2puppetmain.cpp
+++ b/share/qtcreator/qml/qmlpuppet/qml2puppet/qml2puppetmain.cpp
@@ -54,7 +54,7 @@
 #endif
 
 #ifdef Q_OS_WIN
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 namespace {
diff --git a/src/libs/qtcreatorcdbext/pytype.cpp b/src/libs/qtcreatorcdbext/pytype.cpp
index 141175515e1..4c94aee58be 100644
--- a/src/libs/qtcreatorcdbext/pytype.cpp
+++ b/src/libs/qtcreatorcdbext/pytype.cpp
@@ -31,7 +31,7 @@
 #include "stringutils.h"
 #include "symbolgroupvalue.h"
 
-#include <Windows.h>
+#include <windows.h>
 #ifndef _NO_CVCONST_H
 #define _NO_CVCONST_H
 #include <dbghelp.h>
diff --git a/src/libs/qtcreatorcdbext/stringutils.cpp b/src/libs/qtcreatorcdbext/stringutils.cpp
index 5bbd98ed0f0..3ab2ec7e2f2 100644
--- a/src/libs/qtcreatorcdbext/stringutils.cpp
+++ b/src/libs/qtcreatorcdbext/stringutils.cpp
@@ -36,7 +36,7 @@
 #include <codecvt>
 #include <iomanip>
 
-#include <Windows.h>
+#include <windows.h>
 
 static const char whiteSpace[] = " \t\r\n";
 
diff --git a/src/plugins/compilationdatabaseprojectmanager/compilationdatabaseproject.cpp b/src/plugins/compilationdatabaseprojectmanager/compilationdatabaseproject.cpp
index 90ae013eab8..0656dbd8783 100644
--- a/src/plugins/compilationdatabaseprojectmanager/compilationdatabaseproject.cpp
+++ b/src/plugins/compilationdatabaseprojectmanager/compilationdatabaseproject.cpp
@@ -54,7 +54,7 @@
 #include <QFileDialog>
 
 #ifdef Q_OS_WIN
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 using namespace ProjectExplorer;
diff --git a/src/tools/winrtdebughelper/winrtdebughelper.cpp b/src/tools/winrtdebughelper/winrtdebughelper.cpp
index 79bf3280ae2..f871dbf345d 100644
--- a/src/tools/winrtdebughelper/winrtdebughelper.cpp
+++ b/src/tools/winrtdebughelper/winrtdebughelper.cpp
@@ -23,7 +23,7 @@
 **
 ****************************************************************************/
 
-#include <Windows.h>
+#include <windows.h>
 #include <stdio.h>
 #include <stdlib.h>
 
diff --git a/tests/manual/cplusplus-tools/main.cpp b/tests/manual/cplusplus-tools/main.cpp
index da625df65fd..4a2a26533fa 100644
--- a/tests/manual/cplusplus-tools/main.cpp
+++ b/tests/manual/cplusplus-tools/main.cpp
@@ -31,7 +31,7 @@
 #include <iostream>
 #include <vector>
 #include <cstdio>
-//#include <Windows.h>
+//#include <windows.h>
 //#include <linux/version.h>
 #include "dummy.h"
 #include "detail/header.h"