diff --git a/src/librbml/lib.rs b/src/librbml/lib.rs
index 28d5e1812f0..bbedbc75395 100644
--- a/src/librbml/lib.rs
+++ b/src/librbml/lib.rs
@@ -499,8 +499,9 @@ pub mod reader {
             Ok(result)
         }
 
-        fn read_enum_variant<T, F>(&mut self, _: &[&str], f: F) -> DecodeResult<T> where
-            F: FnOnce(&mut Decoder<'doc>, uint) -> DecodeResult<T>,
+        fn read_enum_variant<T, F>(&mut self, _: &[&str],
+                                   mut f: F) -> DecodeResult<T>
+            where F: FnMut(&mut Decoder<'doc>, uint) -> DecodeResult<T>,
         {
             debug!("read_enum_variant()");
             let idx = try!(self._next_uint(EsEnumVid));
@@ -526,8 +527,9 @@ pub mod reader {
             f(self)
         }
 
-        fn read_enum_struct_variant<T, F>(&mut self, _: &[&str], f: F) -> DecodeResult<T> where
-            F: FnOnce(&mut Decoder<'doc>, uint) -> DecodeResult<T>,
+        fn read_enum_struct_variant<T, F>(&mut self, _: &[&str],
+                                          mut f: F) -> DecodeResult<T>
+            where F: FnMut(&mut Decoder<'doc>, uint) -> DecodeResult<T>,
         {
             debug!("read_enum_struct_variant()");
             let idx = try!(self._next_uint(EsEnumVid));
@@ -610,8 +612,8 @@ pub mod reader {
             self.read_tuple_arg(idx, f)
         }
 
-        fn read_option<T, F>(&mut self, f: F) -> DecodeResult<T> where
-            F: FnOnce(&mut Decoder<'doc>, bool) -> DecodeResult<T>,
+        fn read_option<T, F>(&mut self, mut f: F) -> DecodeResult<T> where
+            F: FnMut(&mut Decoder<'doc>, bool) -> DecodeResult<T>,
         {
             debug!("read_option()");
             self.read_enum("Option", move |this| {
diff --git a/src/libserialize/json.rs b/src/libserialize/json.rs
index bd634a58382..c811a16e2b1 100644
--- a/src/libserialize/json.rs
+++ b/src/libserialize/json.rs
@@ -2082,8 +2082,9 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self)
     }
 
-    fn read_enum_variant<T, F>(&mut self, names: &[&str], f: F) -> DecodeResult<T> where
-        F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
+    fn read_enum_variant<T, F>(&mut self, names: &[&str],
+                               mut f: F) -> DecodeResult<T>
+        where F: FnMut(&mut Decoder, uint) -> DecodeResult<T>,
     {
         debug!("read_enum_variant(names={})", names);
         let name = match self.pop() {
@@ -2133,7 +2134,7 @@ impl ::Decoder<DecoderError> for Decoder {
     }
 
     fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> DecodeResult<T> where
-        F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
+        F: FnMut(&mut Decoder, uint) -> DecodeResult<T>,
     {
         debug!("read_enum_struct_variant(names={})", names);
         self.read_enum_variant(names, f)
@@ -2230,8 +2231,8 @@ impl ::Decoder<DecoderError> for Decoder {
         self.read_tuple_arg(idx, f)
     }
 
-    fn read_option<T, F>(&mut self, f: F) -> DecodeResult<T> where
-        F: FnOnce(&mut Decoder, bool) -> DecodeResult<T>,
+    fn read_option<T, F>(&mut self, mut f: F) -> DecodeResult<T> where
+        F: FnMut(&mut Decoder, bool) -> DecodeResult<T>,
     {
         debug!("read_option()");
         match self.pop() {
diff --git a/src/libserialize/serialize.rs b/src/libserialize/serialize.rs
index 98bd2f6bc93..0e0d3b4115b 100644
--- a/src/libserialize/serialize.rs
+++ b/src/libserialize/serialize.rs
@@ -120,12 +120,12 @@ pub trait Decoder<E> {
         F: FnOnce(&mut Self) -> Result<T, E>;
 
     fn read_enum_variant<T, F>(&mut self, names: &[&str], f: F) -> Result<T, E> where
-        F: FnOnce(&mut Self, uint) -> Result<T, E>;
+        F: FnMut(&mut Self, uint) -> Result<T, E>;
     fn read_enum_variant_arg<T, F>(&mut self, a_idx: uint, f: F) -> Result<T, E> where
         F: FnOnce(&mut Self) -> Result<T, E>;
 
     fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> Result<T, E> where
-        F: FnOnce(&mut Self, uint) -> Result<T, E>;
+        F: FnMut(&mut Self, uint) -> Result<T, E>;
     fn read_enum_struct_variant_field<T, F>(&mut self,
                                             &f_name: &str,
                                             f_idx: uint,
@@ -154,7 +154,7 @@ pub trait Decoder<E> {
 
     // Specialized types:
     fn read_option<T, F>(&mut self, f: F) -> Result<T, E> where
-        F: FnOnce(&mut Self, bool) -> Result<T, E>;
+        F: FnMut(&mut Self, bool) -> Result<T, E>;
 
     fn read_seq<T, F>(&mut self, f: F) -> Result<T, E> where
         F: FnOnce(&mut Self, uint) -> Result<T, E>;