diff --git a/crates/aiken-project/src/deps/downloader.rs b/crates/aiken-project/src/deps/downloader.rs
index ec15cd45..5dd82d17 100644
--- a/crates/aiken-project/src/deps/downloader.rs
+++ b/crates/aiken-project/src/deps/downloader.rs
@@ -3,7 +3,11 @@ use std::{io::Cursor, path::Path};
 use futures::future;
 use reqwest::Client;
 
-use crate::{config::PackageName, error::Error, paths};
+use crate::{
+    config::PackageName,
+    error::Error,
+    paths::{self, CacheKey},
+};
 
 use super::manifest::Package;
 
@@ -41,15 +45,20 @@ impl<'a> Downloader<'a> {
         &self,
         package: &Package,
     ) -> Result<bool, Error> {
-        self.ensure_package_downloaded(package).await?;
-        self.extract_package_from_cache(&package.name, &package.version)
+        let cache_key = paths::CacheKey::new(&self.http, package).await?;
+        self.ensure_package_downloaded(package, &cache_key).await?;
+        self.extract_package_from_cache(&package.name, &cache_key)
             .await
     }
 
-    pub async fn ensure_package_downloaded(&self, package: &Package) -> Result<bool, Error> {
+    pub async fn ensure_package_downloaded(
+        &self,
+        package: &Package,
+        cache_key: &CacheKey,
+    ) -> Result<bool, Error> {
         let packages_cache_path = paths::packages_cache();
-        let zipball_path =
-            paths::package_cache_zipball(&package.name, &package.version.to_string());
+
+        let zipball_path = paths::package_cache_zipball(cache_key);
 
         if !packages_cache_path.exists() {
             tokio::fs::create_dir_all(packages_cache_path).await?;
@@ -83,7 +92,7 @@ impl<'a> Downloader<'a> {
     pub async fn extract_package_from_cache(
         &self,
         name: &PackageName,
-        version: &str,
+        cache_key: &CacheKey,
     ) -> Result<bool, Error> {
         let destination = self.root_path.join(paths::build_deps_package(name));
 
@@ -94,9 +103,7 @@ impl<'a> Downloader<'a> {
 
         tokio::fs::create_dir_all(&destination).await?;
 
-        let zipball_path = self
-            .root_path
-            .join(paths::package_cache_zipball(name, version));
+        let zipball_path = self.root_path.join(paths::package_cache_zipball(cache_key));
 
         let zipball = tokio::fs::read(zipball_path).await?;
 
diff --git a/crates/aiken-project/src/deps/manifest.rs b/crates/aiken-project/src/deps/manifest.rs
index e0e53ced..0b22b83f 100644
--- a/crates/aiken-project/src/deps/manifest.rs
+++ b/crates/aiken-project/src/deps/manifest.rs
@@ -87,7 +87,7 @@ impl Manifest {
     }
 }
 
-#[derive(Deserialize, Serialize)]
+#[derive(Deserialize, Serialize, Clone)]
 pub struct Package {
     pub name: PackageName,
     pub version: String,
diff --git a/crates/aiken-project/src/error.rs b/crates/aiken-project/src/error.rs
index 3c853d5b..b0b5c7ab 100644
--- a/crates/aiken-project/src/error.rs
+++ b/crates/aiken-project/src/error.rs
@@ -1,4 +1,4 @@
-use crate::{pretty, script::EvalHint};
+use crate::{deps::manifest::Package, pretty, script::EvalHint};
 use aiken_lang::{
     ast::{BinOp, Span},
     parser::error::ParseError,
@@ -106,6 +106,14 @@ pub enum Error {
         src: String,
         evaluation_hint: Option<EvalHint>,
     },
+
+    #[error(
+        "I was unable to resolve '{}' for {}/{}",
+        package.version,
+        package.name.owner,
+        package.name.repo
+    )]
+    UnknownPackageVersion { package: Package },
 }
 
 impl Error {
@@ -187,6 +195,7 @@ impl Error {
             Error::Http(_) => None,
             Error::ZipExtract(_) => None,
             Error::JoinError(_) => None,
+            Error::UnknownPackageVersion { .. } => None,
         }
     }
 
@@ -208,6 +217,7 @@ impl Error {
             Error::Http(_) => None,
             Error::ZipExtract(_) => None,
             Error::JoinError(_) => None,
+            Error::UnknownPackageVersion { .. } => None,
         }
     }
 }
@@ -257,6 +267,7 @@ impl Diagnostic for Error {
             Error::Http(_) => Some(Box::new("aiken::deps")),
             Error::ZipExtract(_) => None,
             Error::JoinError(_) => None,
+            Error::UnknownPackageVersion { .. } => Some(Box::new("aiken::deps")),
         }
     }
 
@@ -312,6 +323,7 @@ impl Diagnostic for Error {
             Error::Http(_) => None,
             Error::ZipExtract(_) => None,
             Error::JoinError(_) => None,
+            Error::UnknownPackageVersion{..} => None,
         }
     }
 
@@ -345,6 +357,7 @@ impl Diagnostic for Error {
             Error::Http(_) => None,
             Error::ZipExtract(_) => None,
             Error::JoinError(_) => None,
+            Error::UnknownPackageVersion { .. } => None,
         }
     }
 
@@ -366,6 +379,7 @@ impl Diagnostic for Error {
             Error::Http(_) => None,
             Error::ZipExtract(_) => None,
             Error::JoinError(_) => None,
+            Error::UnknownPackageVersion { .. } => None,
         }
     }
 
@@ -387,6 +401,7 @@ impl Diagnostic for Error {
             Error::Http { .. } => None,
             Error::ZipExtract { .. } => None,
             Error::JoinError { .. } => None,
+            Error::UnknownPackageVersion { .. } => None,
         }
     }
 }
diff --git a/crates/aiken-project/src/paths.rs b/crates/aiken-project/src/paths.rs
index a5ac9332..4f514e90 100644
--- a/crates/aiken-project/src/paths.rs
+++ b/crates/aiken-project/src/paths.rs
@@ -1,7 +1,8 @@
+use crate::deps::manifest::Package;
+use crate::{config::PackageName, error::Error};
+use reqwest::Client;
 use std::path::PathBuf;
 
-use crate::config::PackageName;
-
 pub fn manifest() -> PathBuf {
     PathBuf::from("aiken.lock")
 }
@@ -22,11 +23,8 @@ pub fn build_deps_package(package_name: &PackageName) -> PathBuf {
     packages().join(format!("{}-{}", package_name.owner, package_name.repo))
 }
 
-pub fn package_cache_zipball(package_name: &PackageName, version: &str) -> PathBuf {
-    packages_cache().join(format!(
-        "{}-{}-{}.zip",
-        package_name.owner, package_name.repo, version
-    ))
+pub fn package_cache_zipball(cache_key: &CacheKey) -> PathBuf {
+    packages_cache().join(cache_key.get_key())
 }
 
 pub fn packages_cache() -> PathBuf {
@@ -38,3 +36,46 @@ pub fn default_aiken_cache() -> PathBuf {
         .expect("Failed to determine user cache directory")
         .join("aiken")
 }
+
+pub struct CacheKey {
+    key: String,
+}
+
+impl CacheKey {
+    pub async fn new(http: &Client, package: &Package) -> Result<CacheKey, Error> {
+        let version = match hex::decode(&package.version) {
+            Ok(..) => Ok(package.version.to_string()),
+            Err(..) => {
+                let url = format!(
+                    "https://api.github.com/repos/{}/{}/zipball/{}",
+                    package.name.owner, package.name.repo, package.version
+                );
+                let response = http
+                    .head(url)
+                    .header("User-Agent", "aiken-lang")
+                    .send()
+                    .await?;
+                let etag = response
+                    .headers()
+                    .get("etag")
+                    .ok_or(Error::UnknownPackageVersion {
+                        package: package.clone(),
+                    })?
+                    .to_str()
+                    .unwrap()
+                    .replace('"', "");
+                Ok(format!("main@{etag}"))
+            }
+        };
+        version.map(|version| CacheKey {
+            key: format!(
+                "{}-{}-{}.zip",
+                package.name.owner, package.name.repo, version
+            ),
+        })
+    }
+
+    pub fn get_key(&self) -> &str {
+        self.key.as_ref()
+    }
+}