diff --git a/src/rustc_serialize/reader.rs b/src/rustc_serialize/reader.rs
index d3dbfb3..1be8304 100644
--- a/src/rustc_serialize/reader.rs
+++ b/src/rustc_serialize/reader.rs
@@ -129,7 +129,10 @@ impl<'a, R: Read> DecoderReader<'a, R> {
 
 impl <'a, A> DecoderReader<'a, A> {
     fn read_bytes(&mut self, count: u64) -> Result<(), DecodingError> {
-        self.read += count;
+        self.read = match self.read.checked_add(count) {
+            Some(read) => read,
+            None => return Err(DecodingError::SizeLimit),
+        };
         match self.size_limit {
             SizeLimit::Infinite => Ok(()),
             SizeLimit::Bounded(x) if self.read <= x => Ok(()),
@@ -342,6 +345,18 @@ impl<'a, R: Read> Decoder for DecoderReader<'a, R> {
         where F: FnOnce(&mut DecoderReader<'a, R>, usize) -> DecodingResult<T>
     {
         let len = try!(self.read_usize());
+        match self.size_limit {
+            SizeLimit::Infinite => (),
+            SizeLimit::Bounded(x) => {
+                let overflow = match self.read.checked_add(len as u64) {
+                    Some(y) => y > x,
+                    None => true,
+                };
+                if overflow {
+                    return Err(DecodingError::SizeLimit);
+                }
+            },
+        };
         f(self, len)
     }
     fn read_seq_elt<T, F>(&mut self, _: usize, f: F) -> DecodingResult<T>
@@ -353,6 +368,18 @@ impl<'a, R: Read> Decoder for DecoderReader<'a, R> {
         where F: FnOnce(&mut DecoderReader<'a, R>, usize) -> DecodingResult<T>
     {
         let len = try!(self.read_usize());
+        match self.size_limit {
+            SizeLimit::Infinite => (),
+            SizeLimit::Bounded(x) => {
+                let overflow = match self.read.checked_add(len as u64) {
+                    Some(y) => y > x,
+                    None => true,
+                };
+                if overflow {
+                    return Err(DecodingError::SizeLimit);
+                }
+            },
+        };
         f(self, len)
     }
     fn read_map_elt_key<T, F>(&mut self, _: usize, f: F) -> DecodingResult<T>