diff --git a/sim/Cargo.toml b/sim/Cargo.toml
index 856ccb2..4644778 100644
--- a/sim/Cargo.toml
+++ b/sim/Cargo.toml
@@ -2,7 +2,7 @@
 name = "bootsim"
 version = "0.1.0"
 authors = ["David Brown <davidb@davidb.org>"]
-edition = "2018"
+edition = "2021"
 
 [features]
 default = []
diff --git a/sim/mcuboot-sys/Cargo.toml b/sim/mcuboot-sys/Cargo.toml
index 1f6b81c..6d21bf5 100644
--- a/sim/mcuboot-sys/Cargo.toml
+++ b/sim/mcuboot-sys/Cargo.toml
@@ -5,7 +5,7 @@
 description = "A simple wrapper around the mcuboot code."
 build = "build.rs"
 publish = false
-edition = "2018"
+edition = "2021"
 
 [features]
 # By default, build with simplistic signature verification.
diff --git a/sim/simflash/Cargo.toml b/sim/simflash/Cargo.toml
index e585d16..972055a 100644
--- a/sim/simflash/Cargo.toml
+++ b/sim/simflash/Cargo.toml
@@ -2,7 +2,7 @@
 name = "simflash"
 version = "0.1.0"
 authors = ["David Brown <david.brown@linaro.org>"]
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 rand = "0.7"