diff --git a/lang/el-compiler/runtime/el_platform_win.h b/lang/el-compiler/runtime/el_platform_win.h
index 88204a0..df42c2b 100644
--- a/lang/el-compiler/runtime/el_platform_win.h
+++ b/lang/el-compiler/runtime/el_platform_win.h
@@ -75,6 +75,7 @@ static inline void* el_win_dlsym(void* handle, const char* name) {
 #include <direct.h>            /* _mkdir */
 #define mkdir(path, mode) _mkdir(path)     /* POSIX mkdir(path,mode) → _mkdir(path) */
 #define timegm _mkgmtime                   /* UTC tm → time_t */
+#define fsync(fd) _commit(fd)              /* no fsync() on Windows; _commit() (<io.h>) is the equiv */
 
 /* setenv/unsetenv: not in the Windows CRT; map to _putenv_s / SetEnvironmentVariable. */
 static inline int setenv(const char* name, const char* value, int overwrite) {
diff --git a/lang/el-compiler/runtime/el_runtime.c b/lang/el-compiler/runtime/el_runtime.c
index 57a9042..c913192 100644
--- a/lang/el-compiler/runtime/el_runtime.c
+++ b/lang/el-compiler/runtime/el_runtime.c
@@ -1963,8 +1963,9 @@ void http_serve_async(el_val_t port, el_val_t handler) {
     int sock = socket(AF_INET6, SOCK_STREAM, 0);
     if (sock < 0) { perror("socket"); return; }
     int yes = 1; int no = 0;
-    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
-    setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &no, sizeof(no));
+    /* Win32/mingw setsockopt takes optval as (const char*); the cast is portable on POSIX too. */
+    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const char*)&yes, sizeof(yes));
+    setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, (const char*)&no, sizeof(no));
     struct sockaddr_in6 addr;
     memset(&addr, 0, sizeof(addr));
     addr.sin6_family = AF_INET6;