diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 3782f9e95194c..ac263ccaca839 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -3543,11 +3543,12 @@ impl<T, A: Allocator> Vec<T, A> {
         //      for item in iterator {
         //          self.push(item);
         //      }
-        while let Some(element) = iterator.next() {
+        let (lower, _) = iterator.size_hint();
+        let initial_len = self.len();
+        iterator.for_each(move |element| {
             let len = self.len();
             if len == self.capacity() {
-                let (lower, _) = iterator.size_hint();
-                self.reserve(lower.saturating_add(1));
+                self.reserve(lower.saturating_sub(len - initial_len).saturating_add(1));
             }
             unsafe {
                 ptr::write(self.as_mut_ptr().add(len), element);
@@ -3556,7 +3557,7 @@ impl<T, A: Allocator> Vec<T, A> {
                 // NB can't overflow since we would have had to alloc the address space
                 self.set_len(len + 1);
             }
-        }
+        });
     }
 
     // specific extend for `TrustedLen` iterators, called both by the specializations