diff --git a/src/content/write.rs b/src/content/write.rs
index 677bb2b..4471c37 100644
--- a/src/content/write.rs
+++ b/src/content/write.rs
@@ -10,6 +10,7 @@ use async_std::task::{self, Context, JoinHandle, Poll};
 use futures::io::AsyncWrite;
 use futures::prelude::*;
 use memmap2::MmapMut;
+// use memmap::MmapMut;
 use ssri::{Algorithm, Integrity, IntegrityOpts};
 use tempfile::NamedTempFile;
 
@@ -121,11 +122,12 @@ impl AsyncWriter {
             .create(&tmp_path)
             .await
             .to_internal()?;
-        let tmpfile = task::spawn_blocking(|| NamedTempFile::new_in(tmp_path))
+        let mut tmpfile = task::spawn_blocking(|| NamedTempFile::new_in(tmp_path))
             .await
             .to_internal()?;
         let mmap = if let Some(size) = size {
             if size <= MAX_MMAP_SIZE {
+                tmpfile.as_file_mut().set_len(size as u64).to_internal()?;
                 unsafe { MmapMut::map_mut(tmpfile.as_file()).ok() }
             } else {
                 None
diff --git a/src/put.rs b/src/put.rs
index ec5ec2d..8670a9b 100644
--- a/src/put.rs
+++ b/src/put.rs
@@ -440,4 +440,34 @@ mod tests {
         let data = crate::read_sync(&dir, "hello").unwrap();
         assert_eq!(data, b"hello");
     }
+
+    #[test]
+    fn hash_write_sync() {
+        let tmp = tempfile::tempdir().unwrap();
+        let dir = tmp.path().to_owned();
+        let original = format!("hello world{}", 5);
+        let integrity = crate::write_hash_sync(&dir, &original)
+            .expect("should be able to write a hash synchronously");
+        let bytes = crate::read_hash_sync(&dir, &integrity)
+            .expect("should be able to read the data we just wrote");
+        let result =
+            String::from_utf8(bytes).expect("we wrote valid utf8 but did not read valid utf8 back");
+        assert_eq!(result, original, "we did not read back what we wrote");
+    }
+
+    #[async_attributes::test]
+    async fn hash_write_async() {
+        let tmp = tempfile::tempdir().unwrap();
+        let dir = tmp.path().to_owned();
+        let original = format!("hello world{}", 12);
+        let integrity = crate::write_hash(&dir, &original)
+            .await
+            .expect("should be able to write a hash asynchronously");
+        let bytes = crate::read_hash(&dir, &integrity)
+            .await
+            .expect("should be able to read back what we wrote");
+        let result =
+            String::from_utf8(bytes).expect("we wrote valid utf8 but did not read valid utf8 back");
+        assert_eq!(result, original, "we did not read back what we wrote");
+    }
 }