diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 9c3645616327412f8b3b0455ca604bde65c44b7d..2c2307315727337ae178581499b0008403f13c4b 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -417,6 +417,25 @@ const Thread = struct {
                     else => unreachable,
                 };
             },
+            .dragonfly => {
+                var timeout_us: c_int = undefined;
+                if (timeout_ns) |ns| {
+                    timeout_us = std.math.cast(c_int, ns / std.time.ns_per_us) orelse std.math.maxInt(c_int);
+                } else {
+                    timeout_us = 0;
+                }
+                if (thread) |t| try t.beginSyscall();
+                const rc = std.c.umtx_sleep(@ptrCast(ptr), @bitCast(expect), timeout_us);
+                if (thread) |t| t.endSyscall();
+                if (is_debug) switch (std.posix.errno(rc)) {
+                    .SUCCESS => {},
+                    .BUSY => {}, // ptr != expect
+                    .AGAIN => {}, // maybe timed out, or paged out, or hit 2s kernel refresh
+                    .INTR => {}, // spurious wake
+                    .INVAL => unreachable, // invalid timeout
+                    else => unreachable,
+                };
+            },
             else => if (std.Thread.use_pthreads) {
                 // TODO integrate the following function being called with robust cancelation.
                 return pthreads_futex.wait(ptr, expect, timeout_ns) catch |err| switch (err) {
@@ -510,6 +529,13 @@ const Thread = struct {
                 );
                 assert(rc >= 0);
             },
+            .dragonfly => {
+                // will generally return 0 unless the address is bad
+                _ = std.c.umtx_wakeup(
+                    @ptrCast(ptr),
+                    @min(max_waiters, std.math.maxInt(c_int)),
+                );
+            },
             else => if (std.Thread.use_pthreads) {
                 return pthreads_futex.wake(ptr, max_waiters);
             } else {