diff --git a/sim/mcuboot-sys/build.rs b/sim/mcuboot-sys/build.rs
index 49739f6..440c4ae 100644
--- a/sim/mcuboot-sys/build.rs
+++ b/sim/mcuboot-sys/build.rs
@@ -178,6 +178,7 @@
             conf.file("../../ext/tinycrypt/lib/source/sha256.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");
         }
 
         if sig_ed25519 {