diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 667446526a0bb4..0d8a638f40cfa4 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -21,7 +21,7 @@
 #endif /* HAVE_SYS_STAT_H */
 
 #ifdef MS_WINDOWS
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 /* Various interned strings */
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index c264d33b0b0f35..ea01a286874baa 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -303,7 +303,7 @@ if_indextoname(index) -- return the corresponding interface name\n\
 # endif
 
 /* Provides the IsWindows7SP1OrGreater() function */
-#include <VersionHelpers.h>
+#include <versionhelpers.h>
 
 /* remove some flags on older version Windows during run-time.
    https://msdn.microsoft.com/en-us/library/windows/desktop/ms738596.aspx */
diff --git a/Tools/msi/bundle/bootstrap/pch.h b/Tools/msi/bundle/bootstrap/pch.h
index 6a66fa5a51ebf7..b0aa5111dabd0d 100644
--- a/Tools/msi/bundle/bootstrap/pch.h
+++ b/Tools/msi/bundle/bootstrap/pch.h
@@ -15,7 +15,7 @@
 
 #include <windows.h>
 #include <gdiplus.h>
-#include <Uxtheme.h>
+#include <uxtheme.h>
 #include <msiquery.h>
 #include <objbase.h>
 #include <shlobj.h>