diff --git a/sim/mcuboot-sys/Cargo.toml b/sim/mcuboot-sys/Cargo.toml
index 3466ff0..cbf05e5 100644
--- a/sim/mcuboot-sys/Cargo.toml
+++ b/sim/mcuboot-sys/Cargo.toml
@@ -47,6 +47,9 @@
 # Support multiple images (currently 2 instead of 1).
 multiimage = []
 
+# Check (in software) against version downgrades.
+downgrade-prevention = []
+
 [build-dependencies]
 cc = "1.0.25"
 
diff --git a/sim/mcuboot-sys/build.rs b/sim/mcuboot-sys/build.rs
index 1c6584f..3bf4409 100644
--- a/sim/mcuboot-sys/build.rs
+++ b/sim/mcuboot-sys/build.rs
@@ -22,6 +22,7 @@
     let enc_ec256 = env::var("CARGO_FEATURE_ENC_EC256").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();
 
     let mut conf = cc::Build::new();
     conf.define("__BOOTSIM__", None);
@@ -31,6 +32,10 @@
     conf.define("MCUBOOT_MAX_IMG_SECTORS", Some("128"));
     conf.define("MCUBOOT_IMAGE_NUMBER", Some(if multiimage { "2" } else { "1" }));
 
+    if downgrade_prevention && !overwrite_only {
+        panic!("Downgrade prevention requires overwrite only");
+    }
+
     if bootstrap {
         conf.define("MCUBOOT_BOOTSTRAP", None);
     }
@@ -39,6 +44,10 @@
         conf.define("MCUBOOT_VALIDATE_PRIMARY_SLOT", None);
     }
 
+    if downgrade_prevention {
+        conf.define("MCUBOOT_DOWNGRADE_PREVENTION", None);
+    }
+
     // Currently no more than one sig type can be used simultaneously.
     if vec![sig_rsa, sig_rsa3072, sig_ecdsa, sig_ed25519].iter()
         .fold(0, |sum, &v| sum + v as i32) > 1 {