diff --git a/otty-pty/Cargo.toml b/otty-pty/Cargo.toml
index 269e8fa..cbca693 100644
--- a/otty-pty/Cargo.toml
+++ b/otty-pty/Cargo.toml
@@ -15,7 +15,10 @@ anyhow = { workspace = true }
 thiserror = { workspace = true }
 log = { workspace = true }
 mio = { workspace = true, features = ["os-ext", "net"] }
-ssh2 = "0.9.5"
+# `openssl-on-win32`: make the Windows build use the (vendored) OpenSSL
+# crypto backend instead of WinCNG. WinCNG offers only finite-field DH key
+# exchange, which modern servers (OpenSSH >= 10) no longer accept.
+ssh2 = { version = "0.9.5", features = ["openssl-on-win32"] }
 # Force a statically-linked (vendored) OpenSSL build. The `ssh2` crate pulls in
 # `libssh2-sys` -> `openssl-sys`, which by default links the host's libssl.
 # Different Ubuntu releases ship incompatible sonames (libssl1.1 on 20.04,