diff --git a/src/spooled.rs b/src/spooled.rs
index 2c8eaa4e5..9b2e7e7b2 100644
--- a/src/spooled.rs
+++ b/src/spooled.rs
@@ -96,7 +96,7 @@ impl SpooledTempFile {
     }
 
     pub fn set_len(&mut self, size: u64) -> Result<(), io::Error> {
-        if size as usize > self.max_size {
+        if size > self.max_size as u64 {
             self.roll()?; // does nothing if already rolled over
         }
         match &mut self.inner {
@@ -157,7 +157,7 @@ impl Write for SpooledTempFile {
         // roll over to file if necessary
         if matches! {
             &self.inner, SpooledData::InMemory(cursor)
-            if cursor.position() as usize + buf.len() > self.max_size
+            if cursor.position().saturating_add(buf.len() as u64) > self.max_size as u64
         } {
             self.roll()?;
         }
@@ -173,8 +173,10 @@ impl Write for SpooledTempFile {
         if matches! {
             &self.inner, SpooledData::InMemory(cursor)
             // Borrowed from the rust standard library.
-            if cursor.position() as usize + bufs.iter()
-                .fold(0usize, |a, b| a.saturating_add(b.len())) > self.max_size
+            if bufs
+                .iter()
+                .fold(cursor.position(), |a, b| a.saturating_add(b.len() as u64))
+                > self.max_size as u64
         } {
             self.roll()?;
         }
diff --git a/src/util.rs b/src/util.rs
index 8c04953a3..e91150f0a 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -5,7 +5,11 @@ use std::{io, iter::repeat_with};
 use crate::error::IoResultExt;
 
 fn tmpname(prefix: &OsStr, suffix: &OsStr, rand_len: usize) -> OsString {
-    let mut buf = OsString::with_capacity(prefix.len() + suffix.len() + rand_len);
+    let capacity = prefix
+        .len()
+        .saturating_add(suffix.len())
+        .saturating_add(rand_len);
+    let mut buf = OsString::with_capacity(capacity);
     buf.push(prefix);
     let mut char_buf = [0u8; 4];
     for c in repeat_with(fastrand::alphanumeric).take(rand_len) {
diff --git a/tests/spooled.rs b/tests/spooled.rs
index a3bcc03d8..406021436 100644
--- a/tests/spooled.rs
+++ b/tests/spooled.rs
@@ -305,3 +305,18 @@ fn test_set_len_rollover() {
     assert_eq!(t.read_to_end(&mut buf).unwrap(), 20);
     assert_eq!(buf.as_slice(), b"abcde\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0");
 }
+
+#[test]
+fn test_write_overflow() {
+    let mut t = spooled_tempfile(10);
+    t.seek(SeekFrom::Start(u64::MAX)).unwrap();
+    assert!(t.write(b"abcde").is_err());
+}
+
+#[cfg(target_pointer_width = "32")]
+#[test]
+fn test_set_len_truncation() {
+    let mut t = spooled_tempfile(100);
+    assert!(t.set_len(usize::MAX as u64 + 5).is_ok());
+    assert!(t.is_rolled());
+}