diff --git a/crates/alexandrie/src/api/crates/publish.rs b/crates/alexandrie/src/api/crates/publish.rs
index d5e4df05..c4607fc1 100644
--- a/crates/alexandrie/src/api/crates/publish.rs
+++ b/crates/alexandrie/src/api/crates/publish.rs
@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 use std::io::Read;
 use std::path::PathBuf;
+use std::pin::pin;
 
 use async_std::io::prelude::*;
 
@@ -171,6 +172,21 @@ fn link_badges(
     Ok(())
 }
 
+/// Checks whether the passed-in reader has ended (meaning it has reached EOF).
+///
+/// This function tests for this by attempting to read one more byte from the passed-in reader.
+/// Therefore, the reader should not be used after having called this function, because that one byte
+/// will be missing from the output.
+async fn has_reader_ended<R>(reader: R) -> std::io::Result<bool>
+where
+    R: async_std::io::Read,
+{
+    pin!(reader)
+        .read(&mut [0])
+        .await
+        .map(|bytes_read| bytes_read == 0)
+}
+
 /// Route to publish a new crate (used by `cargo publish`).
 pub(crate) async fn put(mut req: Request<State>) -> tide::Result {
     let state = req.state().clone();
@@ -191,6 +207,10 @@ pub(crate) async fn put(mut req: Request<State>) -> tide::Result {
             .take(max_crate_size)
             .read_to_end(&mut bytes)
             .await?;
+
+        if !has_reader_ended(&mut req).await? {
+            return Err(Error::from(AlexError::CrateTooLarge { max_crate_size }).into());
+        }
     } else {
         (&mut req).read_to_end(&mut bytes).await?;
     }
diff --git a/crates/alexandrie/src/error.rs b/crates/alexandrie/src/error.rs
index 02fc30ec..f4aa52f4 100644
--- a/crates/alexandrie/src/error.rs
+++ b/crates/alexandrie/src/error.rs
@@ -87,6 +87,14 @@ pub enum AlexError {
         /// The list of missing query parameters.
         missing_params: &'static [&'static str],
     },
+    /// The uploaded crate is larger than the maximum allowed crate size.
+    #[error(
+        "uploaded crate is larger than the maximum allowed crate size of {max_crate_size} bytes"
+    )]
+    CrateTooLarge {
+        /// The maximum allowed crate size (in bytes).
+        max_crate_size: u64,
+    },
 }
 
 // impl IntoResponse for Error {