diff --git a/src/random.h b/src/random.h
index 439226f..c44f52a 100644
--- a/src/random.h
+++ b/src/random.h
@@ -17,7 +17,13 @@
  */
 
 #if defined(_WIN32)
+/*
+ * The defined WIN32_NO_STATUS macro disables return code definitions in
+ * windows.h, which avoids "macro redefinition" MSVC warnings in ntstatus.h.
+ */
+#define WIN32_NO_STATUS
 #include <windows.h>
+#undef WIN32_NO_STATUS
 #include <ntstatus.h>
 #include <bcrypt.h>
 #elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
@@ -36,7 +42,7 @@
 /* Returns 1 on success, and 0 on failure. */
 static int fill_random(unsigned char* data, size_t size) {
 #if defined(_WIN32)
-    NTSTATUS res = BCryptGenRandom(NULL, data, size, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+    NTSTATUS res = BCryptGenRandom(NULL, data, (ULONG)size, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
     if (res != STATUS_SUCCESS || size > ULONG_MAX) {
         return 0;
     } else {