diff --git a/sim/mcuboot-sys/build.rs b/sim/mcuboot-sys/build.rs
index b431cb3..49739f6 100644
--- a/sim/mcuboot-sys/build.rs
+++ b/sim/mcuboot-sys/build.rs
@@ -20,6 +20,7 @@
     let enc_rsa = env::var("CARGO_FEATURE_ENC_RSA").is_ok();
     let enc_kw = env::var("CARGO_FEATURE_ENC_KW").is_ok();
     let enc_ec256 = env::var("CARGO_FEATURE_ENC_EC256").is_ok();
+    let enc_x25519 = env::var("CARGO_FEATURE_ENC_X25519").is_ok();
     let bootstrap = env::var("CARGO_FEATURE_BOOTSTRAP").is_ok();
     let multiimage = env::var("CARGO_FEATURE_MULTIIMAGE").is_ok();
     let downgrade_prevention = env::var("CARGO_FEATURE_DOWNGRADE_PREVENTION").is_ok();
@@ -109,7 +110,7 @@
         conf.file("../../ext/fiat/src/curve25519.c");
         conf.file("../../ext/mbedtls-asn1/src/platform_util.c");
         conf.file("../../ext/mbedtls-asn1/src/asn1parse.c");
-    } else if !enc_ec256 {
+    } else if !enc_ec256 && !enc_x25519 {
         // No signature type, only sha256 validation. The default
         // configuration file bundled with mbedTLS is sufficient.
         // When using ECIES-P256 rely on Tinycrypt.
@@ -214,6 +215,32 @@
         conf.file("../../ext/tinycrypt/lib/source/ecc_dh.c");
     }
 
+    if enc_x25519 {
+        conf.define("MCUBOOT_ENCRYPT_X25519", None);
+        conf.define("MCUBOOT_ENC_IMAGES", None);
+        conf.define("MCUBOOT_USE_TINYCRYPT", None);
+        conf.define("MCUBOOT_SWAP_SAVE_ENCTLV", None);
+
+        conf.file("../../boot/bootutil/src/encrypted.c");
+        conf.file("csupport/keys.c");
+
+        conf.include("../../ext/mbedtls-asn1/include");
+        conf.include("../../ext/tinycrypt/lib/include");
+        conf.include("../../ext/tinycrypt-sha512/lib/include");
+
+        conf.file("../../ext/fiat/src/curve25519.c");
+
+        conf.file("../../ext/tinycrypt/lib/source/utils.c");
+        conf.file("../../ext/tinycrypt/lib/source/sha256.c");
+
+        conf.file("../../ext/mbedtls-asn1/src/platform_util.c");
+        conf.file("../../ext/mbedtls-asn1/src/asn1parse.c");
+
+        conf.file("../../ext/tinycrypt/lib/source/aes_encrypt.c");
+        conf.file("../../ext/tinycrypt/lib/source/aes_decrypt.c");
+        conf.file("../../ext/tinycrypt/lib/source/ctr_mode.c");
+        conf.file("../../ext/tinycrypt/lib/source/hmac.c");
+    }
 
     if sig_rsa && enc_kw {
         conf.define("MBEDTLS_CONFIG_FILE", Some("<config-rsa-kw.h>"));
@@ -221,7 +248,7 @@
         conf.define("MBEDTLS_CONFIG_FILE", Some("<config-rsa.h>"));
     } else if (sig_ecdsa || enc_ec256) && !enc_kw {
         conf.define("MBEDTLS_CONFIG_FILE", Some("<config-asn1.h>"));
-    } else if sig_ed25519 {
+    } else if sig_ed25519 || enc_x25519 {
         conf.define("MBEDTLS_CONFIG_FILE", Some("<config-asn1.h>"));
     } else if enc_kw {
         conf.define("MBEDTLS_CONFIG_FILE", Some("<config-kw.h>"));