diff --git a/ufotofu/src/nb.rs b/ufotofu/src/nb.rs
index c792c2f..6cd3e94 100644
--- a/ufotofu/src/nb.rs
+++ b/ufotofu/src/nb.rs
@@ -423,7 +423,7 @@ where
             let mut produced_so_far = 0;
 
             while produced_so_far < buf.len() {
-                match self.bulk_produce(buf).await {
+                match self.bulk_produce(&mut buf[produced_so_far..]).await {
                     Ok(Left(count)) => produced_so_far += count,
                     Ok(Right(fin)) => {
                         return Err(OverwriteFullSliceError {
diff --git a/ufotofu/src/sync.rs b/ufotofu/src/sync.rs
index 0fede11..19ca01e 100644
--- a/ufotofu/src/sync.rs
+++ b/ufotofu/src/sync.rs
@@ -385,7 +385,7 @@ where
         let mut produced_so_far = 0;
 
         while produced_so_far < buf.len() {
-            match self.bulk_produce(buf) {
+            match self.bulk_produce(&mut buf[produced_so_far..]) {
                 Ok(Left(count)) => produced_so_far += count,
                 Ok(Right(fin)) => {
                     return Err(OverwriteFullSliceError {