diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
index a3a55d8e..74eda4da 100644
--- a/serde/src/private/de.rs
+++ b/serde/src/private/de.rs
@@ -8,7 +8,7 @@
 
 use lib::*;
 
-use de::{Deserialize, DeserializeSeed, Deserializer, Error, IntoDeserializer, Visitor};
+use de::{Deserialize, DeserializeSeed, Deserializer, Error, IntoDeserializer, Visitor, MapAccess};
 
 #[cfg(any(feature = "std", feature = "alloc"))]
 use de::Unexpected;
@@ -2062,3 +2062,117 @@ where
         T::deserialize_in_place(deserializer, self.0)
     }
 }
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub struct FlatMapDeserializer<'a, 'de: 'a, E>(
+    pub &'a mut Vec<Option<(String, Content<'de>)>>,
+    pub PhantomData<E>
+);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de, E> Deserializer<'de> for FlatMapDeserializer<'a, 'de, E>
+    where E: Error
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        Err(Error::custom("can only deserialize structs and maps in flatten mode"))
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_map(FlatMapAccess::new(self.0.iter_mut(), None))
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        _: &'static str,
+        fields: &'static [&'static str],
+        visitor: V
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_map(FlatMapAccess::new(self.0.iter_mut(), Some(fields)))
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 u8 u16 u32 u64 f32 f64 char str string bytes
+        byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct enum identifier ignored_any
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub struct FlatMapAccess<'a, 'de: 'a, E> {
+    iter: slice::IterMut<'a, Option<(String, Content<'de>)>>,
+    pending_content: Option<Content<'de>>,
+    fields: Option<&'static [&'static str]>,
+    _marker: PhantomData<E>,
+}
+
+impl<'a, 'de, E> FlatMapAccess<'a, 'de, E> {
+    fn new(
+        iter: slice::IterMut<'a, Option<(String, Content<'de>)>>,
+        fields: Option<&'static [&'static str]>
+    ) -> FlatMapAccess<'a, 'de, E> {
+        FlatMapAccess {
+            iter: iter,
+            pending_content: None,
+            fields: fields,
+            _marker: PhantomData,
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de, E> MapAccess<'de> for FlatMapAccess<'a, 'de, E>
+    where E: Error
+{
+    type Error = E;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        loop {
+            let item = match self.iter.next() {
+                Some(item) => {
+                    if item.is_some() {
+                        item
+                    } else {
+                        continue;
+                    }
+                }
+                None => return Ok(None)
+            };
+
+            if match self.fields {
+                None => false,
+                Some(fields) if fields.contains(&item.as_ref().unwrap().0.as_str()) => false,
+                _ => true
+            } {
+                continue;
+            }
+
+            let (key, content) = item.take().unwrap();
+            self.pending_content = Some(content);
+            return seed.deserialize(ContentDeserializer::new(Content::String(key))).map(Some);
+        }
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.pending_content.take() {
+            Some(value) => seed.deserialize(ContentDeserializer::new(value)),
+            None => Err(Error::custom("value is missing")),
+        }
+    }
+}
diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
index 01ea6bfe..c9c6989f 100644
--- a/serde_derive/src/de.rs
+++ b/serde_derive/src/de.rs
@@ -2026,7 +2026,7 @@ fn deserialize_map(
     // Collect contents for flatten fields into a buffer
     let let_collect = if cattrs.has_flatten() {
         Some(quote! {
-            let mut __collect = Vec::<(String, _serde::private::de::Content)>::new();
+            let mut __collect = Vec::<Option<(String, _serde::private::de::Content)>>::new();
         })
     } else {
         None
@@ -2070,7 +2070,7 @@ fn deserialize_map(
     let ignored_arm = if cattrs.has_flatten() {
         Some(quote! {
             __Field::__other(__name) => {
-                __collect.push((__name, try!(_serde::de::MapAccess::next_value(&mut __map))));
+                __collect.push(Some((__name, try!(_serde::de::MapAccess::next_value(&mut __map)))));
             }
         })
     } else if cattrs.deny_unknown_fields() {
@@ -2130,7 +2130,7 @@ fn deserialize_map(
 
     let collected_deny_unknown_fields = if cattrs.has_flatten() && cattrs.deny_unknown_fields() {
         Some(quote! {
-            if let Some((__key, _)) = __collect.into_iter().next() {
+            if let Some(Some((__key, _))) = __collect.into_iter().filter(|x| x.is_some()).next() {
                 return _serde::export::Err(
                     _serde::de::Error::unknown_field_in_flattened_structure(&__key));
             }