diff --git a/rust-no-heap/Cargo.toml b/rust-no-heap/Cargo.toml
index 5d8aee2..0d5f95f 100644
--- a/rust-no-heap/Cargo.toml
+++ b/rust-no-heap/Cargo.toml
@@ -1,4 +1,5 @@
 [package]
+edition = "2015"
 name = "qrcodegen-no-heap"
 version = "1.8.1"
 authors = ["Project Nayuki"]
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 95807ce..3498fdd 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -1,4 +1,5 @@
 [package]
+edition = "2015"
 name = "qrcodegen"
 version = "1.8.0"
 authors = ["Project Nayuki"]