diff --git a/mxshadowsrv.c b/mxshadowsrv.c
index d8a5910..9d1b423 100644
--- a/mxshadowsrv.c
+++ b/mxshadowsrv.c
@@ -69,11 +69,11 @@ static void unmap_shadow(char *shadow_buf, struct stat *statbuf) {
 #define MAX_THREADS 8
 #define TIMEOUT 30000     // client timeout in msec
 
-pthread_mutex_t shadow_mutex = PTHREAD_MUTEX_INITIALIZER ;
-char *shadow_buf = NULL;   // protected by shadow_mutex
-struct stat statbuf;       // protected by shadow_mutex
-SSL_CTX *ssl_ctx;
-sem_t free_worker;
+static pthread_mutex_t shadow_mutex = PTHREAD_MUTEX_INITIALIZER ;
+static char *shadow_buf = NULL;   // protected by shadow_mutex
+static struct stat statbuf;       // protected by shadow_mutex
+static SSL_CTX *ssl_ctx;
+static sem_t free_worker;
 #ifdef DEBUG_MAX_CONNECTS
 static int debug_remaining_connects = DEBUG_MAX_CONNECTS;
 #endif
@@ -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));