diff --git a/acme_common/build.rs b/acme_common/build.rs
index beef778..d159ea9 100644
--- a/acme_common/build.rs
+++ b/acme_common/build.rs
@@ -6,15 +6,18 @@ macro_rules! set_rustc_env_var {
     }};
 }
 
+#[allow(clippy::unusual_byte_groupings)]
 fn main() {
-    if env::var("DEP_OPENSSL_VERSION_NUMBER").is_ok() {
-        println!("cargo:rustc-cfg=ed25519");
-        println!("cargo:rustc-cfg=ed448");
+    if let Ok(v) = env::var("DEP_OPENSSL_VERSION_NUMBER") {
+        let version = u64::from_str_radix(&v, 16).unwrap();
+        // OpenSSL 1.1.1
+        if version >= 0x1_01_01_00_0 {
+            println!("cargo:rustc-cfg=ed25519");
+            println!("cargo:rustc-cfg=ed448");
+        }
         set_rustc_env_var!("ACMED_TLS_LIB_NAME", "OpenSSL");
     }
     if env::var("DEP_OPENSSL_LIBRESSL_VERSION_NUMBER").is_ok() {
-        println!("cargo:rustc-cfg=ed25519");
-        println!("cargo:rustc-cfg=ed448");
         set_rustc_env_var!("ACMED_TLS_LIB_NAME", "LibreSSL");
     }
 }