diff --git a/crypto/bio/fd.c b/crypto/bio/fd.c
index c40056d1..da43fba8 100644
--- a/crypto/bio/fd.c
+++ b/crypto/bio/fd.c
@@ -60,6 +60,8 @@
 
 #if !defined(OPENSSL_WINDOWS)
 #include <unistd.h>
+#else
+#include <Windows.h>
 #endif
 
 #include <openssl/buf.h>
diff --git a/crypto/err/err.c b/crypto/err/err.c
index a06e159c..fd3a76bf 100644
--- a/crypto/err/err.c
+++ b/crypto/err/err.c
@@ -114,6 +114,10 @@
 #include <stdarg.h>
 #include <stdio.h>
 
+#if defined(OPENSSL_WINDOWS)
+#include <Windows.h>
+#endif
+
 #include <openssl/lhash.h>
 #include <openssl/mem.h>
 #include <openssl/thread.h>
diff --git a/crypto/thread.c b/crypto/thread.c
index 6472cd3f..15e38bdd 100644
--- a/crypto/thread.c
+++ b/crypto/thread.c
@@ -58,6 +58,10 @@
 
 #include <errno.h>
 
+#if defined(OPENSSL_WINDOWS)
+#include <Windows.h>
+#endif
+
 #include <openssl/mem.h>
 #include <openssl/type_check.h>