diff --git a/testutil/Cargo.toml b/testutil/Cargo.toml
index 4b715f9699..3676e3610a 100644
--- a/testutil/Cargo.toml
+++ b/testutil/Cargo.toml
@@ -13,6 +13,9 @@ edition = "2021"
 
 [dependencies]
 cargo_metadata = "0.18.0"
+# Pin to 0.1.5 because more recent versions require a Rust version more recent
+# than our MSRV.
+cargo-platform = "=0.1.5"
 rustc_version = "0.4.0"
 # Pin to 0.3.0 because more recent versions require a Rust version more recent
 # than our MSRV.