diff --git a/include/polarssl/md5.h b/include/polarssl/md5.h
index 936e9c9..2e97c2b 100644
--- a/include/polarssl/md5.h
+++ b/include/polarssl/md5.h
@@ -29,6 +29,13 @@
 
 #include <string.h>
 
+#ifdef _MSC_VER
+#include <basetsd.h>
+typedef UINT32 uint32_t;
+#else
+#include <inttypes.h>
+#endif
+
 #define POLARSSL_ERR_MD5_FILE_IO_ERROR                 -0x0074  /**< Read/write error in file. */
 
 /**
@@ -36,8 +43,8 @@
  */
 typedef struct
 {
-    unsigned long total[2];     /*!< number of bytes processed  */
-    unsigned long state[4];     /*!< intermediate digest state  */
+    uint32_t total[2];          /*!< number of bytes processed  */
+    uint32_t state[4];          /*!< intermediate digest state  */
     unsigned char buffer[64];   /*!< data block being processed */
 
     unsigned char ipad[64];     /*!< HMAC: inner padding        */