diff --git a/std/os.zig b/std/os.zig
index 9ff2e8f87f..c2010bf6a9 100644
--- a/std/os.zig
+++ b/std/os.zig
@@ -133,6 +133,11 @@ fn getRandomBytesDevURandom(buf: []u8) !void {
     const fd = try openC(c"/dev/urandom", O_RDONLY | O_CLOEXEC, 0);
     defer close(fd);
 
+    const st = try fstat(fd);
+    if (!S_ISCHR(st.mode)) {
+        return error.NoDevice;
+    }
+
     const stream = &std.fs.File.openHandle(fd).inStream().stream;
     stream.readNoEof(buf) catch return error.Unexpected;
 }
diff --git a/std/os/bits/darwin.zig b/std/os/bits/darwin.zig
index b8d229dbe9..483d4cda90 100644
--- a/std/os/bits/darwin.zig
+++ b/std/os/bits/darwin.zig
@@ -1116,3 +1116,62 @@ pub const stack_t = extern struct {
     ss_size: isize,
     ss_flags: i32,
 };
+
+pub const S_IFMT = 0o170000;
+
+pub const S_IFIFO = 0o010000;
+pub const S_IFCHR = 0o020000;
+pub const S_IFDIR = 0o040000;
+pub const S_IFBLK = 0o060000;
+pub const S_IFREG = 0o100000;
+pub const S_IFLNK = 0o120000;
+pub const S_IFSOCK = 0o140000;
+pub const S_IFWHT = 0o160000;
+
+pub const S_ISUID = 0o4000;
+pub const S_ISGID = 0o2000;
+pub const S_ISVTX = 0o1000;
+pub const S_IRWXU = 0o700;
+pub const S_IRUSR = 0o400;
+pub const S_IWUSR = 0o200;
+pub const S_IXUSR = 0o100;
+pub const S_IRWXG = 0o070;
+pub const S_IRGRP = 0o040;
+pub const S_IWGRP = 0o020;
+pub const S_IXGRP = 0o010;
+pub const S_IRWXO = 0o007;
+pub const S_IROTH = 0o004;
+pub const S_IWOTH = 0o002;
+pub const S_IXOTH = 0o001;
+
+pub fn S_ISFIFO(m: u32) bool {
+    return m & S_IFMT == S_IFIFO;
+}
+
+pub fn S_ISCHR(m: u32) bool {
+    return m & S_IFMT == S_IFCHR;
+}
+
+pub fn S_ISDIR(m: u32) bool {
+    return m & S_IFMT == S_IFDIR;
+}
+
+pub fn S_ISBLK(m: u32) bool {
+    return m & S_IFMT == S_IFBLK;
+}
+
+pub fn S_ISREG(m: u32) bool {
+    return m & S_IFMT == S_IFREG;
+}
+
+pub fn S_ISLNK(m: u32) bool {
+    return m & S_IFMT == S_IFLNK;
+}
+
+pub fn S_ISSOCK(m: u32) bool {
+    return m & S_IFMT == S_IFSOCK;
+}
+
+pub fn S_IWHT(m: u32) bool {
+    return m & S_IFMT == S_IFWHT;
+}
diff --git a/std/os/bits/freebsd.zig b/std/os/bits/freebsd.zig
index 198857983e..45432a6c07 100644
--- a/std/os/bits/freebsd.zig
+++ b/std/os/bits/freebsd.zig
@@ -876,3 +876,62 @@ pub const stack_t = extern struct {
     ss_size: isize,
     ss_flags: i32,
 };
+
+pub const S_IFMT = 0o170000;
+
+pub const S_IFIFO = 0o010000;
+pub const S_IFCHR = 0o020000;
+pub const S_IFDIR = 0o040000;
+pub const S_IFBLK = 0o060000;
+pub const S_IFREG = 0o100000;
+pub const S_IFLNK = 0o120000;
+pub const S_IFSOCK = 0o140000;
+pub const S_IFWHT = 0o160000;
+
+pub const S_ISUID = 0o4000;
+pub const S_ISGID = 0o2000;
+pub const S_ISVTX = 0o1000;
+pub const S_IRWXU = 0o700;
+pub const S_IRUSR = 0o400;
+pub const S_IWUSR = 0o200;
+pub const S_IXUSR = 0o100;
+pub const S_IRWXG = 0o070;
+pub const S_IRGRP = 0o040;
+pub const S_IWGRP = 0o020;
+pub const S_IXGRP = 0o010;
+pub const S_IRWXO = 0o007;
+pub const S_IROTH = 0o004;
+pub const S_IWOTH = 0o002;
+pub const S_IXOTH = 0o001;
+
+pub fn S_ISFIFO(m: u32) bool {
+    return m & S_IFMT == S_IFIFO;
+}
+
+pub fn S_ISCHR(m: u32) bool {
+    return m & S_IFMT == S_IFCHR;
+}
+
+pub fn S_ISDIR(m: u32) bool {
+    return m & S_IFMT == S_IFDIR;
+}
+
+pub fn S_ISBLK(m: u32) bool {
+    return m & S_IFMT == S_IFBLK;
+}
+
+pub fn S_ISREG(m: u32) bool {
+    return m & S_IFMT == S_IFREG;
+}
+
+pub fn S_ISLNK(m: u32) bool {
+    return m & S_IFMT == S_IFLNK;
+}
+
+pub fn S_ISSOCK(m: u32) bool {
+    return m & S_IFMT == S_IFSOCK;
+}
+
+pub fn S_IWHT(m: u32) bool {
+    return m & S_IFMT == S_IFWHT;
+}
diff --git a/std/os/darwin.zig b/std/os/darwin.zig
index 67ce9a06cf..c2b6801e22 100644
--- a/std/os/darwin.zig
+++ b/std/os/darwin.zig
@@ -5,3 +5,4 @@ pub const is_the_target = switch (builtin.os) {
     else => false,
 };
 pub usingnamespace std.c;
+pub usingnamespace @import("bits.zig");
\ No newline at end of file
diff --git a/std/os/freebsd.zig b/std/os/freebsd.zig
index d418ccd415..e9efe64920 100644
--- a/std/os/freebsd.zig
+++ b/std/os/freebsd.zig
@@ -2,3 +2,4 @@ const std = @import("../std.zig");
 const builtin = @import("builtin");
 pub const is_the_target = builtin.os == .freebsd;
 pub usingnamespace std.c;
+pub usingnamespace @import("bits.zig");
\ No newline at end of file