diff --git a/src/lib/libsockfs.js b/src/lib/libsockfs.js
index 7ada365896fdc..10cf2afc65629 100644
--- a/src/lib/libsockfs.js
+++ b/src/lib/libsockfs.js
@@ -421,6 +421,14 @@ addToLibrary({
             }
             {{{ makeSetValue('arg', '0', 'bytes', 'i32') }}};
             return 0;
+          case {{{ cDefs.FIONBIO }}}:
+            var on = {{{ makeGetValue('arg', '0', 'i32') }}};
+            if (on) {
+              sock.stream.flags |= {{{ cDefs.O_NONBLOCK }}};
+            } else {
+              sock.stream.flags &= ~{{{ cDefs.O_NONBLOCK }}};
+            }
+            return 0;
           default:
             return {{{ cDefs.EINVAL }}};
         }
diff --git a/src/lib/libsyscall.js b/src/lib/libsyscall.js
index 6e11512f27e18..61af4001bd53f 100644
--- a/src/lib/libsyscall.js
+++ b/src/lib/libsyscall.js
@@ -284,6 +284,7 @@ var SyscallsLibrary = {
         if (!stream.tty) return -{{{ cDefs.ENOTTY }}};
         return -{{{ cDefs.EINVAL }}}; // not supported
       }
+      case {{{ cDefs.FIONBIO }}}:
       case {{{ cDefs.FIONREAD }}}: {
         var argp = syscallGetVarargP();
         return FS.ioctl(stream, op, argp);
diff --git a/src/struct_info.json b/src/struct_info.json
index 4a6f2a812a25f..e94e38326b46e 100644
--- a/src/struct_info.json
+++ b/src/struct_info.json
@@ -312,6 +312,7 @@
     {
         "file": "bits/ioctl.h",
         "defines": [
+            "FIONBIO",
             "FIONREAD",
             "TCGETA",
             "TCGETS",
diff --git a/src/struct_info_generated.json b/src/struct_info_generated.json
index 3595af1b6d7a5..a31f2e572669e 100644
--- a/src/struct_info_generated.json
+++ b/src/struct_info_generated.json
@@ -292,6 +292,7 @@
         "EWOULDBLOCK": 6,
         "EXDEV": 75,
         "EXFULL": 115,
+        "FIONBIO": 21537,
         "FIONREAD": 21531,
         "F_DUPFD": 0,
         "F_GETFD": 1,
diff --git a/src/struct_info_generated_wasm64.json b/src/struct_info_generated_wasm64.json
index 31ab797e96a84..b3fdd4c8208f0 100644
--- a/src/struct_info_generated_wasm64.json
+++ b/src/struct_info_generated_wasm64.json
@@ -292,6 +292,7 @@
         "EWOULDBLOCK": 6,
         "EXDEV": 75,
         "EXFULL": 115,
+        "FIONBIO": 21537,
         "FIONREAD": 21531,
         "F_DUPFD": 0,
         "F_GETFD": 1,
diff --git a/test/sockets/test_sockets_echo_server.c b/test/sockets/test_sockets_echo_server.c
index 8465ccbbf42cf..151a793b10324 100644
--- a/test/sockets/test_sockets_echo_server.c
+++ b/test/sockets/test_sockets_echo_server.c
@@ -29,6 +29,15 @@ typedef int socklen_t;
 #include <emscripten.h>
 #endif
 
+#ifdef _WIN32
+typedef u_long ioctlarg_t;
+#else
+#define INVALID_SOCKET -1
+#define SOCKET_ERROR -1
+#define ioctlsocket ioctl
+typedef int ioctlarg_t;
+#endif
+
 #include "test_sockets_msg.h"
 
 typedef enum {
@@ -193,16 +202,16 @@ int main() {
 #else
   server.fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 #endif
-  if (server.fd == -1) {
+  if (server.fd == INVALID_SOCKET) {
     perror("cannot create socket");
     exit(EXIT_FAILURE);
   }
-#ifdef _WIN32
-  unsigned long nonblocking = 1;
-  ioctlsocket(server.fd, FIONBIO, &nonblocking);
-#else
-  fcntl(server.fd, F_SETFL, O_NONBLOCK);
-#endif
+
+  ioctlarg_t on = 1;
+  if (ioctlsocket(server.fd, FIONBIO, &on) == SOCKET_ERROR) {
+    perror("ioctlsocket failed");
+    exit(EXIT_FAILURE);
+  }
 
   memset(&addr, 0, sizeof(addr));
   addr.sin_family = AF_INET;
@@ -213,14 +222,14 @@ int main() {
   }
 
   res = bind(server.fd, (struct sockaddr *)&addr, sizeof(addr));
-  if (res == -1) {
+  if (res == SOCKET_ERROR) {
     perror("bind failed");
     exit(EXIT_FAILURE);
   }
 
 #if !TEST_DGRAM
   res = listen(server.fd, 50);
-  if (res == -1) {
+  if (res == SOCKET_ERROR) {
     perror("listen failed");
     exit(EXIT_FAILURE);
   }