diff --git a/core/daemons.c b/core/daemons.c
index 1239cf1a..a8796d67 100644
--- a/core/daemons.c
+++ b/core/daemons.c
@@ -215,7 +215,7 @@ void uwsgi_spawn_daemon(struct uwsgi_daemon *ud) {
 			exit(1);
 		}
 		if (devnull != 0) {
-			if (dup2(devnull, 0)) {
+			if (dup2(devnull, 0) < 0) {
 				uwsgi_error("dup2()");
 				exit(1);
 			}
diff --git a/core/emperor.c b/core/emperor.c
index b922ebaa..db72e049 100644
--- a/core/emperor.c
+++ b/core/emperor.c
@@ -729,7 +729,7 @@ void emperor_add(struct uwsgi_emperor_scanner *ues, char *name, time_t born, cha
 			exit(1);
 		}
 		if (stdin_fd != 0) {
-			if (dup2(stdin_fd, 0)) {
+			if (dup2(stdin_fd, 0) < 0) {
 				uwsgi_error("dup2()");
 				exit(1);
 			}
diff --git a/core/socket.c b/core/socket.c
index d88703e4..ef294025 100644
--- a/core/socket.c
+++ b/core/socket.c
@@ -1632,7 +1632,7 @@ void uwsgi_map_sockets() {
 				exit(1);
 			}
 			if (fd != uwsgi_sock->fd) {
-				if (dup2(fd, uwsgi_sock->fd)) {
+				if (dup2(fd, uwsgi_sock->fd) < 0) {
 					uwsgi_error("dup2()");
 					exit(1);
 				}
@@ -1744,7 +1744,7 @@ void uwsgi_bind_sockets() {
 				exit(1);
 			}
 			if (fd != 0) {
-				if (dup2(fd, 0)) {
+				if (dup2(fd, 0) < 0) {
 					uwsgi_error("dup2()");
 					exit(1);
 				}
diff --git a/core/utils.c b/core/utils.c
index 6fc0694d..57ef1bfb 100644
--- a/core/utils.c
+++ b/core/utils.c
@@ -3335,7 +3335,7 @@ pid_t uwsgi_run_command(char *command, int *stdin_fd, int stdout_fd) {
 			}
 			else {
 				if (in_fd != 0) {
-					if (dup2(in_fd, 0)) {
+					if (dup2(in_fd, 0) < 0) {
 						uwsgi_error("dup2()");
 					}
 				}
diff --git a/core/uwsgi.c b/core/uwsgi.c
index 2dca85c9..3e9dba5e 100644
--- a/core/uwsgi.c
+++ b/core/uwsgi.c
@@ -2738,7 +2738,7 @@ next2:
 		}
 
 		if (uwsgi.sockets->fd != 0) {
-			if (dup2(uwsgi.sockets->fd, 0)) {
+			if (dup2(uwsgi.sockets->fd, 0) < 0) {
 				uwsgi_error("dup2()");
 			}
 		}