diff --git a/src/buf/buf_mut.rs b/src/buf/buf_mut.rs
index fb3623d25..fb00bdf11 100644
--- a/src/buf/buf_mut.rs
+++ b/src/buf/buf_mut.rs
@@ -1034,15 +1034,15 @@ unsafe impl BufMut for Vec<u8> {
 
     #[inline]
     fn bytes_mut(&mut self) -> &mut UninitSlice {
-        if self.capacity() == self.len() {
+        let len = self.len();
+        if self.capacity() == len {
             self.reserve(64); // Grow the vec
         }
 
         let cap = self.capacity();
-        let len = self.len();
 
         let ptr = self.as_mut_ptr();
-        unsafe { &mut UninitSlice::from_raw_parts_mut(ptr, cap)[len..] }
+        unsafe { UninitSlice::from_raw_parts_mut(ptr.add(len), cap - len) }
     }
 
     // Specialize these methods so they can skip checking `remaining_mut`
@@ -1069,6 +1069,7 @@ unsafe impl BufMut for Vec<u8> {
         }
     }
 
+    #[inline]
     fn put_slice(&mut self, src: &[u8]) {
         self.extend_from_slice(src);
     }