diff --git a/Cargo.toml b/Cargo.toml
index 2ea461e..ecd6229 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,10 +15,11 @@ resolver = "2"
 features = ["nightly"]
 
 [dependencies]
-# "digest" is exempt from SemVer but breaking changes will bump minor versions
+# "digest" (pre-1.0.0) is exempt from SemVer but breaking changes will bump minor versions
+# (see https://github.com/dalek-cryptography/curve25519-dalek/tree/main/curve25519-dalek#stable)
 # (see https://github.com/dalek-cryptography/curve25519-dalek/tree/main/curve25519-dalek#public-api-semver-exemptions)
-# so only allow patch changes
-curve25519-dalek = { version = "~4.0", default-features = false, features = ["alloc", "digest", "zeroize", "precomputed-tables"] }
+# so only allow patch changes inside known compatible range
+curve25519-dalek = { version = ">= 4.0, < 4.2", default-features = false, features = ["alloc", "digest", "zeroize", "precomputed-tables"] }
 der = { version = "0.7.1", optional = true }
 ed25519 = { version = "2.2.0", default-features = false }
 hashbrown = "0.14.0"
diff --git a/rust-toolchain b/rust-toolchain
index 902c741..832e9af 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-1.65.0
+1.70.0