diff --git a/examples/pdf-mod-info.cc b/examples/pdf-mod-info.cc
index 84cb818f..ca0fe26a 100644
--- a/examples/pdf-mod-info.cc
+++ b/examples/pdf-mod-info.cc
@@ -10,7 +10,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #ifdef _WIN32
-#include <Windows.h>
+#include <windows.h>
 #include <direct.h>
 #include <io.h>
 #else
diff --git a/libqpdf/QUtil.cc b/libqpdf/QUtil.cc
index f451290e..37cfda9e 100644
--- a/libqpdf/QUtil.cc
+++ b/libqpdf/QUtil.cc
@@ -19,7 +19,7 @@
 #include <string.h>
 #include <fcntl.h>
 #ifdef _WIN32
-#include <Windows.h>
+#include <windows.h>
 #include <direct.h>
 #include <io.h>
 #else
diff --git a/libqpdf/SecureRandomDataProvider.cc b/libqpdf/SecureRandomDataProvider.cc
index 0b0b6c73..ca891036 100644
--- a/libqpdf/SecureRandomDataProvider.cc
+++ b/libqpdf/SecureRandomDataProvider.cc
@@ -3,11 +3,11 @@
 #include <qpdf/qpdf-config.h>
 #include <qpdf/QUtil.hh>
 #ifdef _WIN32
-# include <Windows.h>
+# include <windows.h>
 # include <direct.h>
 # include <io.h>
 # ifndef SKIP_OS_SECURE_RANDOM
-#  include <Wincrypt.h>
+#  include <wincrypt.h>
 # endif
 #endif