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 30001754fe576b..3a439c4bfadc30 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/Modules/socketmodule.h b/Modules/socketmodule.h
index fdb4e871cef81e..bce74c3da8fd90 100644
--- a/Modules/socketmodule.h
+++ b/Modules/socketmodule.h
@@ -28,7 +28,7 @@
  * I use SIO_GET_MULTICAST_FILTER to detect a decent SDK.
  */
 # ifdef SIO_GET_MULTICAST_FILTER
-#  include <MSTcpIP.h> /* for SIO_RCVALL */
+#  include <mstcpip.h> /* for SIO_RCVALL */
 #  define HAVE_ADDRINFO
 #  define HAVE_SOCKADDR_STORAGE
 #  define HAVE_GETADDRINFO
diff --git a/PC/getpathp.c b/PC/getpathp.c
index df4cb0a20e3577..deda8c9ce9dc0d 100644
--- a/PC/getpathp.c
+++ b/PC/getpathp.c
@@ -89,7 +89,7 @@
 #endif
 
 #include <windows.h>
-#include <Shlwapi.h>
+#include <shlwapi.h>
 
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
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>