diff --git a/ChangeLog.d/net_poll-fd_setsize.txt b/ChangeLog.d/net_poll-fd_setsize.txt
new file mode 100644
index 000000000..e4db8c7e3
--- /dev/null
+++ b/ChangeLog.d/net_poll-fd_setsize.txt
@@ -0,0 +1,4 @@
+Security
+   * Fix a stack buffer overflow with mbedtls_net_poll() and
+     mbedtls_net_recv_timeout() when given a file descriptor that is
+     beyond FD_SETSIZE. Reported by FigBug in #4169.
diff --git a/library/net_sockets.c b/library/net_sockets.c
index 54c2b472f..375434abd 100644
--- a/library/net_sockets.c
+++ b/library/net_sockets.c
@@ -465,6 +465,13 @@ int mbedtls_net_poll( mbedtls_net_context *ctx, uint32_t rw, uint32_t timeout )
     if( fd < 0 )
         return( MBEDTLS_ERR_NET_INVALID_CONTEXT );
 
+    /* A limitation of select() is that it only works with file descriptors
+     * up to FD_SETSIZE. This is a limitation of the fd_set type. Error out
+     * early, because attempting to call FD_SET on a large file descriptor
+     * is a buffer overflow on typical platforms. */
+    if( fd >= FD_SETSIZE )
+        return( MBEDTLS_ERR_NET_POLL_FAILED );
+
 #if defined(__has_feature)
 #if __has_feature(memory_sanitizer)
     /* Ensure that memory sanitizers consider read_fds and write_fds as
@@ -584,6 +591,13 @@ int mbedtls_net_recv_timeout( void *ctx, unsigned char *buf,
     if( fd < 0 )
         return( MBEDTLS_ERR_NET_INVALID_CONTEXT );
 
+    /* A limitation of select() is that it only works with file descriptors
+     * up to FD_SETSIZE. This is a limitation of the fd_set type. Error out
+     * early, because attempting to call FD_SET on a large file descriptor
+     * is a buffer overflow on typical platforms. */
+    if( fd >= FD_SETSIZE )
+        return( MBEDTLS_ERR_NET_POLL_FAILED );
+
     FD_ZERO( &read_fds );
     FD_SET( fd, &read_fds );