diff --git a/src/common.cpp b/src/common.cpp
index 4c88ca4fc..98fc57238 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -2091,6 +2091,9 @@ bool fish_reserved_codepoint(wchar_t c) {
 void redirect_tty_output() {
     struct termios t;
     int fd = open("/dev/null", O_WRONLY);
+    if (fd == -1) {
+        __fish_assert("Could not open /dev/null!", __FILE__, __LINE__, errno);
+    }
     if (tcgetattr(STDIN_FILENO, &t) == -1 && errno == EIO) dup2(fd, STDIN_FILENO);
     if (tcgetattr(STDOUT_FILENO, &t) == -1 && errno == EIO) dup2(fd, STDOUT_FILENO);
     if (tcgetattr(STDERR_FILENO, &t) == -1 && errno == EIO) dup2(fd, STDERR_FILENO);