diff --git a/crates/cache-key/src/cache_key.rs b/crates/cache-key/src/cache_key.rs
index f1880c5be..019c54eb5 100644
--- a/crates/cache-key/src/cache_key.rs
+++ b/crates/cache-key/src/cache_key.rs
@@ -8,6 +8,7 @@ use std::num::{
 use std::path::{Path, PathBuf};
 
 use seahash::SeaHasher;
+use url::Url;
 
 /// A trait for types that can be hashed in a stable way across versions and platforms. Equivalent
 /// to Ruff's [`CacheKey`] trait.
@@ -211,6 +212,13 @@ impl CacheKey for PathBuf {
     }
 }
 
+impl CacheKey for Url {
+    #[inline]
+    fn cache_key(&self, state: &mut CacheKeyHasher) {
+        self.as_str().cache_key(state);
+    }
+}
+
 impl<T: CacheKey> CacheKey for Option<T> {
     #[inline]
     fn cache_key(&self, state: &mut CacheKeyHasher) {
diff --git a/crates/distribution-types/src/file.rs b/crates/distribution-types/src/file.rs
index 0a0fcb81c..0011af614 100644
--- a/crates/distribution-types/src/file.rs
+++ b/crates/distribution-types/src/file.rs
@@ -4,7 +4,6 @@ use std::path::PathBuf;
 use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};
 use thiserror::Error;
-use url::Url;
 
 use pep440_rs::{VersionSpecifiers, VersionSpecifiersParseError};
 use pep508_rs::VerbatimUrl;
@@ -42,10 +41,11 @@ impl File {
             requires_python: file.requires_python.transpose()?,
             size: file.size,
             upload_time: file.upload_time,
-            url: FileLocation::Url(
-                base.join_relative(&file.url)
-                    .map_err(|err| FileConversionError::Url(file.url.clone(), err))?,
-            ),
+            url: if file.url.contains("://") {
+                FileLocation::AbsoluteUrl(file.url)
+            } else {
+                FileLocation::RelativeUrl(base.clone(), file.url)
+            },
             yanked: file.yanked,
         })
     }
@@ -55,7 +55,9 @@ impl File {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub enum FileLocation {
     /// URL relative to the base URL.
-    Url(Url),
+    RelativeUrl(BaseUrl, String),
+    /// Absolute URL.
+    AbsoluteUrl(String),
     /// Absolute path to a file.
     Path(PathBuf, VerbatimUrl),
 }
@@ -63,7 +65,8 @@ pub enum FileLocation {
 impl Display for FileLocation {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         match self {
-            FileLocation::Url(url) => Display::fmt(url, f),
+            FileLocation::RelativeUrl(_base, url) => Display::fmt(&url, f),
+            FileLocation::AbsoluteUrl(url) => Display::fmt(&url, f),
             FileLocation::Path(path, _url) => Display::fmt(&path.display(), f),
         }
     }
diff --git a/crates/distribution-types/src/lib.rs b/crates/distribution-types/src/lib.rs
index 5a487807f..bba1cebb8 100644
--- a/crates/distribution-types/src/lib.rs
+++ b/crates/distribution-types/src/lib.rs
@@ -694,17 +694,49 @@ impl Identifier for Path {
     }
 }
 
+impl Identifier for String {
+    fn distribution_id(&self) -> DistributionId {
+        DistributionId::new(cache_key::digest(&self))
+    }
+
+    fn resource_id(&self) -> ResourceId {
+        ResourceId::new(cache_key::digest(&self))
+    }
+}
+
+impl Identifier for &str {
+    fn distribution_id(&self) -> DistributionId {
+        DistributionId::new(cache_key::digest(&self))
+    }
+
+    fn resource_id(&self) -> ResourceId {
+        ResourceId::new(cache_key::digest(&self))
+    }
+}
+
+impl Identifier for (&Url, &str) {
+    fn distribution_id(&self) -> DistributionId {
+        DistributionId::new(cache_key::digest(&self))
+    }
+
+    fn resource_id(&self) -> ResourceId {
+        ResourceId::new(cache_key::digest(&self))
+    }
+}
+
 impl Identifier for FileLocation {
     fn distribution_id(&self) -> DistributionId {
         match self {
-            FileLocation::Url(url) => url.distribution_id(),
+            FileLocation::RelativeUrl(base, url) => (base.as_url(), url.as_str()).distribution_id(),
+            FileLocation::AbsoluteUrl(url) => url.distribution_id(),
             FileLocation::Path(path, _) => path.distribution_id(),
         }
     }
 
     fn resource_id(&self) -> ResourceId {
         match self {
-            FileLocation::Url(url) => url.resource_id(),
+            FileLocation::RelativeUrl(base, url) => (base.as_url(), url.as_str()).resource_id(),
+            FileLocation::AbsoluteUrl(url) => url.resource_id(),
             FileLocation::Path(path, _) => path.resource_id(),
         }
     }
diff --git a/crates/pep508-rs/src/verbatim_url.rs b/crates/pep508-rs/src/verbatim_url.rs
index eb1736ffc..e5610a159 100644
--- a/crates/pep508-rs/src/verbatim_url.rs
+++ b/crates/pep508-rs/src/verbatim_url.rs
@@ -13,6 +13,10 @@ use url::Url;
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct VerbatimUrl {
     /// The parsed URL.
+    #[serde(
+        serialize_with = "Url::serialize_internal",
+        deserialize_with = "Url::deserialize_internal"
+    )]
     url: Url,
     /// The URL as it was provided by the user.
     #[derivative(PartialEq = "ignore")]
diff --git a/crates/puffin-client/src/registry_client.rs b/crates/puffin-client/src/registry_client.rs
index ad0360376..837b5af0c 100644
--- a/crates/puffin-client/src/registry_client.rs
+++ b/crates/puffin-client/src/registry_client.rs
@@ -225,8 +225,14 @@ impl RegistryClient {
     pub async fn wheel_metadata(&self, built_dist: &BuiltDist) -> Result<Metadata21, Error> {
         let metadata = match &built_dist {
             BuiltDist::Registry(wheel) => match &wheel.file.url {
-                FileLocation::Url(url) => {
-                    self.wheel_metadata_registry(&wheel.index, &wheel.file, url)
+                FileLocation::RelativeUrl(base, url) => {
+                    let url = base.join_relative(url)?;
+                    self.wheel_metadata_registry(&wheel.index, &wheel.file, &url)
+                        .await?
+                }
+                FileLocation::AbsoluteUrl(url) => {
+                    let url = Url::parse(url)?;
+                    self.wheel_metadata_registry(&wheel.index, &wheel.file, &url)
                         .await?
                 }
                 FileLocation::Path(path, _url) => {
diff --git a/crates/puffin-distribution/src/distribution_database.rs b/crates/puffin-distribution/src/distribution_database.rs
index 59fe29c5f..21530c6d5 100644
--- a/crates/puffin-distribution/src/distribution_database.rs
+++ b/crates/puffin-distribution/src/distribution_database.rs
@@ -111,7 +111,11 @@ impl<'a, Context: BuildContext + Send + Sync> DistributionDatabase<'a, Context>
         match &dist {
             Dist::Built(BuiltDist::Registry(wheel)) => {
                 let url = match &wheel.file.url {
-                    FileLocation::Url(url) => url,
+                    FileLocation::RelativeUrl(base, url) => base
+                        .join_relative(url)
+                        .map_err(|err| DistributionDatabaseError::Url(url.clone(), err))?,
+                    FileLocation::AbsoluteUrl(url) => Url::parse(url)
+                        .map_err(|err| DistributionDatabaseError::Url(url.clone(), err))?,
                     FileLocation::Path(path, url) => {
                         let cache_entry = self.cache.entry(
                             CacheBucket::Wheels,
@@ -143,7 +147,7 @@ impl<'a, Context: BuildContext + Send + Sync> DistributionDatabase<'a, Context>
                 // for downloading and unzipping (with a buffer in between) and switch
                 // to rayon if this buffer grows large by the time the file is fully
                 // downloaded.
-                let reader = self.client.stream_external(url).await?;
+                let reader = self.client.stream_external(&url).await?;
 
                 // Download and unzip the wheel to a temporary directory.
                 let temp_dir = tempfile::tempdir_in(self.cache.root())?;
diff --git a/crates/puffin-distribution/src/source/mod.rs b/crates/puffin-distribution/src/source/mod.rs
index 4ba7b4c1a..733c18d65 100644
--- a/crates/puffin-distribution/src/source/mod.rs
+++ b/crates/puffin-distribution/src/source/mod.rs
@@ -99,7 +99,11 @@ impl<'a, T: BuildContext> SourceDistCachedBuilder<'a, T> {
             }
             SourceDist::Registry(registry_source_dist) => {
                 let url = match &registry_source_dist.file.url {
-                    FileLocation::Url(url) => url,
+                    FileLocation::RelativeUrl(base, url) => base
+                        .join_relative(url)
+                        .map_err(|err| SourceDistError::UrlParse(url.clone(), err))?,
+                    FileLocation::AbsoluteUrl(url) => Url::parse(url)
+                        .map_err(|err| SourceDistError::UrlParse(url.clone(), err))?,
                     FileLocation::Path(path, url) => {
                         let path_source_dist = PathSourceDist {
                             name: registry_source_dist.filename.name.clone(),
@@ -123,7 +127,7 @@ impl<'a, T: BuildContext> SourceDistCachedBuilder<'a, T> {
                 self.url(
                     source_dist,
                     &registry_source_dist.file.filename,
-                    url,
+                    &url,
                     &cache_shard,
                     None,
                 )
@@ -168,7 +172,11 @@ impl<'a, T: BuildContext> SourceDistCachedBuilder<'a, T> {
             }
             SourceDist::Registry(registry_source_dist) => {
                 let url = match &registry_source_dist.file.url {
-                    FileLocation::Url(url) => url,
+                    FileLocation::RelativeUrl(base, url) => base
+                        .join_relative(url)
+                        .map_err(|err| SourceDistError::UrlParse(url.clone(), err))?,
+                    FileLocation::AbsoluteUrl(url) => Url::parse(url)
+                        .map_err(|err| SourceDistError::UrlParse(url.clone(), err))?,
                     FileLocation::Path(path, url) => {
                         let path_source_dist = PathSourceDist {
                             name: registry_source_dist.filename.name.clone(),
@@ -192,7 +200,7 @@ impl<'a, T: BuildContext> SourceDistCachedBuilder<'a, T> {
                 self.url_metadata(
                     source_dist,
                     &registry_source_dist.file.filename,
-                    url,
+                    &url,
                     &cache_shard,
                     None,
                 )
diff --git a/crates/pypi-types/src/base_url.rs b/crates/pypi-types/src/base_url.rs
index 4701bce26..15ea0a63d 100644
--- a/crates/pypi-types/src/base_url.rs
+++ b/crates/pypi-types/src/base_url.rs
@@ -2,7 +2,13 @@ use serde::{Deserialize, Serialize};
 use url::Url;
 
 #[derive(Debug, Clone, Hash, Eq, PartialEq, Serialize, Deserialize)]
-pub struct BaseUrl(Url);
+pub struct BaseUrl(
+    #[serde(
+        serialize_with = "Url::serialize_internal",
+        deserialize_with = "Url::deserialize_internal"
+    )]
+    Url,
+);
 
 impl BaseUrl {
     /// Parse the given URL. If it's relative, join it to the current [`BaseUrl`]. Allows for
@@ -19,6 +25,11 @@ impl BaseUrl {
             }
         }
     }
+
+    /// Return the underlying [`Url`].
+    pub fn as_url(&self) -> &Url {
+        &self.0
+    }
 }
 
 impl From<Url> for BaseUrl {