diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index bc71307..0ccc34f 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -50,26 +50,41 @@
 
 #include <windows.h>
 #if _WIN32_WINNT >= 0x0501 /* _WIN32_WINNT_WINXP */
-#include <wincrypt.h>
+#include <bcrypt.h>
+#if _MSC_VER <= 1600
+/* Visual Studio 2010 and earlier issue a warning when both <stdint.h> and <intsafe.h> are included, as they
+ * redefine a number of <TYPE>_MAX constants. These constants are guaranteed to be the same, though, so
+ * we suppress the warning when including intsafe.h.
+ */
+#pragma warning( push )
+#pragma warning( disable : 4005 )
+#endif
+#include <intsafe.h>
+#if _MSC_VER <= 1600
+#pragma warning( pop )
+#endif
 
 int mbedtls_platform_entropy_poll(void *data, unsigned char *output, size_t len,
                                   size_t *olen)
 {
-    HCRYPTPROV provider;
+    ULONG len_as_ulong = 0;
     ((void) data);
     *olen = 0;
 
-    if (CryptAcquireContext(&provider, NULL, NULL,
-                            PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) == FALSE) {
-        return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
+    /*
+     * BCryptGenRandom takes ULONG for size, which is smaller than size_t on 64-bit platforms.
+     * Ensure len's value can be safely converted into a ULONG.
+     */
+    if ( FAILED( SizeTToULong( len, &len_as_ulong ) ) )
+    {
+        return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
     }
 
-    if (CryptGenRandom(provider, (DWORD) len, output) == FALSE) {
-        CryptReleaseContext(provider, 0);
-        return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
+    if ( !BCRYPT_SUCCESS( BCryptGenRandom( NULL, output, len_as_ulong, BCRYPT_USE_SYSTEM_PREFERRED_RNG ) ) )
+    {
+        return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
     }
 
-    CryptReleaseContext(provider, 0);
     *olen = len;
 
     return 0;