diff --git a/README.md b/README.md
index e981c47..7fd9f9f 100644
--- a/README.md
+++ b/README.md
@@ -63,4 +63,5 @@ expected output. Bonus points if it is formatted as a dart test.
 ## References
 
 * https://letsencrypt.org/docs/a-warm-welcome-to-asn1-and-der/
-* https://luca.ntop.org/Teaching/Appunti/asn1.html
\ No newline at end of file
+* https://luca.ntop.org/Teaching/Appunti/asn1.html
+* https://ldap.com/ldapv3-wire-protocol-reference-asn1-ber/
\ No newline at end of file
diff --git a/pubspec.yaml b/pubspec.yaml
index c64b67d..b0170b1 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -3,7 +3,7 @@ version: 1.4.1
 description: An ASN1 parser library for Dart. Encodes / decodes from ASN1 Objects to BER bytes
 homepage: https://github.com/wstrange/asn1lib
 environment:
- sdk: '>=2.12.0 <3.0.0'
+ sdk: '>=2.12.0 <4.0.0'
 
 dev_dependencies:
   test: ^1.22.0