diff --git a/mongoose.c b/mongoose.c
index 80a7df48..1c236204 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -3045,8 +3045,8 @@ static void mg_set_non_blocking_mode(SOCKET fd) {
 #elif MG_ARCH == MG_ARCH_AZURERTOS
   fcntl(fd, F_SETFL, O_NONBLOCK);
 #else
-  fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);  // Set non-blocking mode
-  fcntl(fd, F_SETFD, FD_CLOEXEC);                       // Set close-on-exec
+  fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);  // Non-blocking mode
+  fcntl(fd, F_SETFD, FD_CLOEXEC);                          // Set close-on-exec
 #endif
 }
 
diff --git a/src/sock.c b/src/sock.c
index d103b024..d13a22c9 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -174,8 +174,8 @@ static void mg_set_non_blocking_mode(SOCKET fd) {
 #elif MG_ARCH == MG_ARCH_AZURERTOS
   fcntl(fd, F_SETFL, O_NONBLOCK);
 #else
-  fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);  // Set non-blocking mode
-  fcntl(fd, F_SETFD, FD_CLOEXEC);                       // Set close-on-exec
+  fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);  // Non-blocking mode
+  fcntl(fd, F_SETFD, FD_CLOEXEC);                          // Set close-on-exec
 #endif
 }