diff --git a/mxshadowsrv.c b/mxshadowsrv.c
index d8a5910..fc5044c 100644
--- a/mxshadowsrv.c
+++ b/mxshadowsrv.c
@@ -249,7 +249,7 @@ int main(int argc, char **argv) {
     if (SSL_CTX_use_certificate_file(ssl_ctx, cert_file, SSL_FILETYPE_PEM) <= 0) { psslerror("SSL_CTX_use_certificate_file"); return 1; }
 
     int listen_socket = socket(AF_INET, SOCK_STREAM, 0);
-    if (listen_socket == 0) { perror("socket"); return 1; }
+    if (listen_socket == -1) { perror("socket"); return 1; }
 
     static int true = 1;
     int status = setsockopt(listen_socket, SOL_SOCKET, SO_REUSEADDR, &true, sizeof(true));