diff --git a/src/syscall/fs.rs b/src/syscall/fs.rs
index 49b364b472..005b2494c3 100644
--- a/src/syscall/fs.rs
+++ b/src/syscall/fs.rs
@@ -311,15 +311,32 @@ pub fn dup(fd: FileHandle, buf: UserSliceRo, token: &mut CleanLockToken) -> Resu
 /// Duplicate a file descriptor, placing into a specific fd slot (upstream 0.9.0).
 pub fn dup_into(
     fd: FileHandle,
-    new_fd: FileHandle,
+    new_cd: FileHandle,
     buf: UserSliceRo,
     token: &mut CleanLockToken,
 ) -> Result<FileHandle> {
-    let new_file = duplicate_file(fd, buf, false, token)?;
+    crate::info!("dup_into: fd={:#x} new_cd={:#x} buf_len={}", fd.get(), new_cd.get(), buf.len());
+    let new_file = match duplicate_file(fd, buf, false, token) {
+        Ok(f) => f,
+        Err(e) => {
+            crate::info!("dup_into: duplicate_file failed: {}", e);
+            return Err(e);
+        }
+    };
+    crate::info!("dup_into: duplicate_file ok, inserting at new_cd={:#x}", new_cd.get());
     let current_lock = context::current();
     let mut current = current_lock.read(token.token());
     let (context, mut token) = current.token_split();
-    context.insert_file(new_fd, new_file, &mut token).ok_or(Error::new(EEXIST))
+    match context.insert_file(new_cd, new_file, &mut token) {
+        Some(h) => {
+            crate::info!("dup_into: insert ok, handle={:#x}", h.get());
+            Ok(h)
+        }
+        None => {
+            crate::info!("dup_into: insert_file returned None (EEXIST)");
+            Err(Error::new(EEXIST))
+        }
+    }
 }
 
 /// Duplicate file descriptor, replacing another