diff --git a/src/rcore.rs b/src/rcore.rs
index 9bd7d5e..d6d9565 100644
--- a/src/rcore.rs
+++ b/src/rcore.rs
@@ -76,7 +76,7 @@ pub trait Factory<'a, Ctx: Context<'a>>: 'a + Send + Sync + Clone {
         addresses: &mut Addresses,
     ) -> ParseResult<'a, Ctx, Self>;
     /// Called by finite stream parsers if there's any data left.
-    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> Result<Self::Mtbl, Self::ParseError>;
+    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self>;
 }
 
 pub type Mtbl<'a, Ctx, F> = <F as Factory<'a, Ctx>>::Mtbl;
diff --git a/src/rstd/atomic/atomic_object.rs b/src/rstd/atomic/atomic_object.rs
index 9b008e9..f2a37ad 100644
--- a/src/rstd/atomic/atomic_object.rs
+++ b/src/rstd/atomic/atomic_object.rs
@@ -81,7 +81,7 @@ impl<'a, Ctx: Context<'a>, A: Atomic> Factory<'a, Ctx> for AtomicFactory<A> {
         Ok(A::a_deserialize(deserializer)?.into())
     }
 
-    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         Ok(A::a_extend(mentionable.atomic, tail)?.into())
     }
 }
diff --git a/src/rstd/collections/stack.rs b/src/rstd/collections/stack.rs
index ac14123..fca8955 100644
--- a/src/rstd/collections/stack.rs
+++ b/src/rstd/collections/stack.rs
@@ -102,11 +102,7 @@ impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for StackNodeFa
         Ok(StackNode { rest, element })
     }
 
-    fn extend(
-        &self,
-        mut mentionable: Self::Mtbl,
-        tail: &[u8],
-    ) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, mut mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         mentionable.element = self
             .element_factory
             .extend(mentionable.element, tail)
diff --git a/src/rstd/collections/tree.rs b/src/rstd/collections/tree.rs
index f0bdb14..b628aaa 100644
--- a/src/rstd/collections/tree.rs
+++ b/src/rstd/collections/tree.rs
@@ -151,11 +151,7 @@ impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for NodeFactory
         Ok(Node { l, r, key })
     }
 
-    fn extend(
-        &self,
-        mut mentionable: Self::Mtbl,
-        tail: &[u8],
-    ) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, mut mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         mentionable.key = self
             .0
             .extend(mentionable.key, tail)
@@ -182,11 +178,7 @@ impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for TreeFactory
         Ok(tree)
     }
 
-    fn extend(
-        &self,
-        mut mentionable: Self::Mtbl,
-        tail: &[u8],
-    ) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, mut mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         mentionable.height = u64::a_extend(mentionable.height, tail)?;
         mentionable.validate_height()?;
         Ok(mentionable)
diff --git a/src/rstd/inlining/static_pair.rs b/src/rstd/inlining/static_pair.rs
index 939fdb7..8c6f073 100644
--- a/src/rstd/inlining/static_pair.rs
+++ b/src/rstd/inlining/static_pair.rs
@@ -151,7 +151,7 @@ impl<'a, Ctx: Context<'a>, SP: StaticPair<'a, Ctx>> Factory<'a, Ctx>
         })
     }
 
-    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         let (_, fb) = SP::factories(&self.factory_data);
         let (a, b) = mentionable.pair.into_elements();
         match fb.extend(b, tail) {
diff --git a/src/rstd/nullable.rs b/src/rstd/nullable.rs
index 2012e9f..9fed7af 100644
--- a/src/rstd/nullable.rs
+++ b/src/rstd/nullable.rs
@@ -70,11 +70,7 @@ impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for NullableFac
         })
     }
 
-    fn extend(
-        &self,
-        _mentionable: Self::Mtbl,
-        tail: &[u8],
-    ) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, _mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         Err(PointParseError::WrongLength(HASH_SIZE + tail.len()))
     }
 }
diff --git a/src/rstd/point.rs b/src/rstd/point.rs
index efc20aa..31c7426 100644
--- a/src/rstd/point.rs
+++ b/src/rstd/point.rs
@@ -76,11 +76,7 @@ impl<'a, Ctx: Context<'a>, F: Factory<'a, Ctx>> Factory<'a, Ctx> for PointFactor
         Ok(addresses.next_point(deserializer, resolver, self.factory.clone())?)
     }
 
-    fn extend(
-        &self,
-        _mentionable: Self::Mtbl,
-        tail: &[u8],
-    ) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, _mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         Err(PointParseError::WrongLength(HASH_SIZE + tail.len()))
     }
 }
diff --git a/src/rstd/typeless.rs b/src/rstd/typeless.rs
index bbfdcfd..7ba44f3 100644
--- a/src/rstd/typeless.rs
+++ b/src/rstd/typeless.rs
@@ -107,7 +107,7 @@ impl<'a, Ctx: Context<'a>> Factory<'a, Ctx> for TypelessFactory<'a, Ctx> {
         }
     }
 
-    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> Result<Self::Mtbl, Self::ParseError> {
+    fn extend(&self, mentionable: Self::Mtbl, tail: &[u8]) -> ParseResult<'a, Ctx, Self> {
         self.t_extend.xt(mentionable, tail)
     }
 }