diff --git a/tokio/src/stream/collect.rs b/tokio/src/stream/collect.rs
index 46494287cd8..a2b5169f365 100644
--- a/tokio/src/stream/collect.rs
+++ b/tokio/src/stream/collect.rs
@@ -19,7 +19,7 @@ pin_project! {
     {
         #[pin]
         stream: T,
-        collection: U::Collection,
+        collection: U::InternalCollection,
     }
 }
 
@@ -42,7 +42,7 @@ where
 {
     pub(super) fn new(stream: T) -> Collect<T, U> {
         let (lower, upper) = stream.size_hint();
-        let collection = U::initialize(lower, upper);
+        let collection = U::initialize(sealed::Internal, lower, upper);
 
         Collect { stream, collection }
     }
@@ -64,12 +64,12 @@ where
             let item = match ready!(me.stream.poll_next(cx)) {
                 Some(item) => item,
                 None => {
-                    return Ready(U::finalize(&mut me.collection));
+                    return Ready(U::finalize(sealed::Internal, &mut me.collection));
                 }
             };
 
-            if !U::extend(&mut me.collection, item) {
-                return Ready(U::finalize(&mut me.collection));
+            if !U::extend(sealed::Internal, &mut me.collection, item) {
+                return Ready(U::finalize(sealed::Internal, &mut me.collection));
             }
         }
     }
@@ -80,32 +80,32 @@ where
 impl FromStream<()> for () {}
 
 impl sealed::FromStreamPriv<()> for () {
-    type Collection = ();
+    type InternalCollection = ();
 
-    fn initialize(_lower: usize, _upper: Option<usize>) {}
+    fn initialize(_: sealed::Internal, _lower: usize, _upper: Option<usize>) {}
 
-    fn extend(_collection: &mut (), _item: ()) -> bool {
+    fn extend(_: sealed::Internal, _collection: &mut (), _item: ()) -> bool {
         true
     }
 
-    fn finalize(_collection: &mut ()) {}
+    fn finalize(_: sealed::Internal, _collection: &mut ()) {}
 }
 
 impl<T: AsRef<str>> FromStream<T> for String {}
 
 impl<T: AsRef<str>> sealed::FromStreamPriv<T> for String {
-    type Collection = String;
+    type InternalCollection = String;
 
-    fn initialize(_lower: usize, _upper: Option<usize>) -> String {
+    fn initialize(_: sealed::Internal, _lower: usize, _upper: Option<usize>) -> String {
         String::new()
     }
 
-    fn extend(collection: &mut String, item: T) -> bool {
+    fn extend(_: sealed::Internal, collection: &mut String, item: T) -> bool {
         collection.push_str(item.as_ref());
         true
     }
 
-    fn finalize(collection: &mut String) -> String {
+    fn finalize(_: sealed::Internal, collection: &mut String) -> String {
         mem::replace(collection, String::new())
     }
 }
@@ -113,18 +113,18 @@ impl<T: AsRef<str>> sealed::FromStreamPriv<T> for String {
 impl<T> FromStream<T> for Vec<T> {}
 
 impl<T> sealed::FromStreamPriv<T> for Vec<T> {
-    type Collection = Vec<T>;
+    type InternalCollection = Vec<T>;
 
-    fn initialize(lower: usize, _upper: Option<usize>) -> Vec<T> {
+    fn initialize(_: sealed::Internal, lower: usize, _upper: Option<usize>) -> Vec<T> {
         Vec::with_capacity(lower)
     }
 
-    fn extend(collection: &mut Vec<T>, item: T) -> bool {
+    fn extend(_: sealed::Internal, collection: &mut Vec<T>, item: T) -> bool {
         collection.push(item);
         true
     }
 
-    fn finalize(collection: &mut Vec<T>) -> Vec<T> {
+    fn finalize(_: sealed::Internal, collection: &mut Vec<T>) -> Vec<T> {
         mem::replace(collection, vec![])
     }
 }
@@ -132,18 +132,19 @@ impl<T> sealed::FromStreamPriv<T> for Vec<T> {
 impl<T> FromStream<T> for Box<[T]> {}
 
 impl<T> sealed::FromStreamPriv<T> for Box<[T]> {
-    type Collection = Vec<T>;
+    type InternalCollection = Vec<T>;
 
-    fn initialize(lower: usize, upper: Option<usize>) -> Vec<T> {
-        <Vec<T> as sealed::FromStreamPriv<T>>::initialize(lower, upper)
+    fn initialize(_: sealed::Internal, lower: usize, upper: Option<usize>) -> Vec<T> {
+        <Vec<T> as sealed::FromStreamPriv<T>>::initialize(sealed::Internal, lower, upper)
     }
 
-    fn extend(collection: &mut Vec<T>, item: T) -> bool {
-        <Vec<T> as sealed::FromStreamPriv<T>>::extend(collection, item)
+    fn extend(_: sealed::Internal, collection: &mut Vec<T>, item: T) -> bool {
+        <Vec<T> as sealed::FromStreamPriv<T>>::extend(sealed::Internal, collection, item)
     }
 
-    fn finalize(collection: &mut Vec<T>) -> Box<[T]> {
-        <Vec<T> as sealed::FromStreamPriv<T>>::finalize(collection).into_boxed_slice()
+    fn finalize(_: sealed::Internal, collection: &mut Vec<T>) -> Box<[T]> {
+        <Vec<T> as sealed::FromStreamPriv<T>>::finalize(sealed::Internal, collection)
+            .into_boxed_slice()
     }
 }
 
@@ -153,18 +154,26 @@ impl<T, U, E> sealed::FromStreamPriv<Result<T, E>> for Result<U, E>
 where
     U: FromStream<T>,
 {
-    type Collection = Result<U::Collection, E>;
-
-    fn initialize(lower: usize, upper: Option<usize>) -> Result<U::Collection, E> {
-        Ok(U::initialize(lower, upper))
+    type InternalCollection = Result<U::InternalCollection, E>;
+
+    fn initialize(
+        _: sealed::Internal,
+        lower: usize,
+        upper: Option<usize>,
+    ) -> Result<U::InternalCollection, E> {
+        Ok(U::initialize(sealed::Internal, lower, upper))
     }
 
-    fn extend(collection: &mut Self::Collection, item: Result<T, E>) -> bool {
+    fn extend(
+        _: sealed::Internal,
+        collection: &mut Self::InternalCollection,
+        item: Result<T, E>,
+    ) -> bool {
         assert!(collection.is_ok());
         match item {
             Ok(item) => {
                 let collection = collection.as_mut().ok().expect("invalid state");
-                U::extend(collection, item)
+                U::extend(sealed::Internal, collection, item)
             }
             Err(err) => {
                 *collection = Err(err);
@@ -173,11 +182,11 @@ where
         }
     }
 
-    fn finalize(collection: &mut Self::Collection) -> Result<U, E> {
+    fn finalize(_: sealed::Internal, collection: &mut Self::InternalCollection) -> Result<U, E> {
         if let Ok(collection) = collection.as_mut() {
-            Ok(U::finalize(collection))
+            Ok(U::finalize(sealed::Internal, collection))
         } else {
-            let res = mem::replace(collection, Ok(U::initialize(0, Some(0))));
+            let res = mem::replace(collection, Ok(U::initialize(sealed::Internal, 0, Some(0))));
 
             if let Err(err) = res {
                 Err(err)
@@ -191,18 +200,18 @@ where
 impl<T: Buf> FromStream<T> for Bytes {}
 
 impl<T: Buf> sealed::FromStreamPriv<T> for Bytes {
-    type Collection = BytesMut;
+    type InternalCollection = BytesMut;
 
-    fn initialize(_lower: usize, _upper: Option<usize>) -> BytesMut {
+    fn initialize(_: sealed::Internal, _lower: usize, _upper: Option<usize>) -> BytesMut {
         BytesMut::new()
     }
 
-    fn extend(collection: &mut BytesMut, item: T) -> bool {
+    fn extend(_: sealed::Internal, collection: &mut BytesMut, item: T) -> bool {
         collection.put(item);
         true
     }
 
-    fn finalize(collection: &mut BytesMut) -> Bytes {
+    fn finalize(_: sealed::Internal, collection: &mut BytesMut) -> Bytes {
         mem::replace(collection, BytesMut::new()).freeze()
     }
 }
@@ -210,18 +219,18 @@ impl<T: Buf> sealed::FromStreamPriv<T> for Bytes {
 impl<T: Buf> FromStream<T> for BytesMut {}
 
 impl<T: Buf> sealed::FromStreamPriv<T> for BytesMut {
-    type Collection = BytesMut;
+    type InternalCollection = BytesMut;
 
-    fn initialize(_lower: usize, _upper: Option<usize>) -> BytesMut {
+    fn initialize(_: sealed::Internal, _lower: usize, _upper: Option<usize>) -> BytesMut {
         BytesMut::new()
     }
 
-    fn extend(collection: &mut BytesMut, item: T) -> bool {
+    fn extend(_: sealed::Internal, collection: &mut BytesMut, item: T) -> bool {
         collection.put(item);
         true
     }
 
-    fn finalize(collection: &mut BytesMut) -> BytesMut {
+    fn finalize(_: sealed::Internal, collection: &mut BytesMut) -> BytesMut {
         mem::replace(collection, BytesMut::new())
     }
 }
@@ -230,17 +239,26 @@ pub(crate) mod sealed {
     #[doc(hidden)]
     pub trait FromStreamPriv<T> {
         /// Intermediate type used during collection process
-        type Collection;
+        ///
+        /// The name of this type is internal and cannot be relied upon.
+        type InternalCollection;
 
         /// Initialize the collection
-        fn initialize(lower: usize, upper: Option<usize>) -> Self::Collection;
+        fn initialize(
+            internal: Internal,
+            lower: usize,
+            upper: Option<usize>,
+        ) -> Self::InternalCollection;
 
         /// Extend the collection with the received item
         ///
         /// Return `true` to continue streaming, `false` complete collection.
-        fn extend(collection: &mut Self::Collection, item: T) -> bool;
+        fn extend(internal: Internal, collection: &mut Self::InternalCollection, item: T) -> bool;
 
         /// Finalize collection into target type.
-        fn finalize(collection: &mut Self::Collection) -> Self;
+        fn finalize(internal: Internal, collection: &mut Self::InternalCollection) -> Self;
     }
+
+    #[allow(missing_debug_implementations)]
+    pub struct Internal;
 }