diff --git a/Cargo.toml b/Cargo.toml
index bab9c09..c545cfd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -49,7 +49,7 @@ byteorder = { version = "^1.2.3", default-features = false, features = ["i128"]
 digest = { version = "0.8", default-features = false }
 clear_on_drop = "=0.2.3"
 subtle = { version = "2", default-features = false }
-serde = { version = "1.0", optional = true }
+serde = { version = "1.0", default-features = false, optional = true }
 packed_simd = { version = "0.3.0", features = ["into_bits"], optional = true }
 
 [build-dependencies]
@@ -58,7 +58,7 @@ byteorder = { version = "^1.2.3", default-features = false, features = ["i128"]
 digest = { version = "0.8", default-features = false }
 clear_on_drop = "=0.2.3"
 subtle = { version = "2", default-features = false }
-serde = { version = "1.0", optional = true }
+serde = { version = "1.0", default-features = false, optional = true }
 packed_simd = { version = "0.3.0", features = ["into_bits"], optional = true }
 
 [features]