diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index b5c0d42b1..451a4ee77 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -179,7 +179,7 @@ where
         let (combined_lower, combined_upper) =
             size_hint::mul_scalar(size_hint::min(curr_hint, next_hint), 2);
         let lower = if curr_lower > next_lower {
-            combined_lower + 1
+            combined_lower.saturating_add(1)
         } else {
             combined_lower
         };
diff --git a/tests/test_std.rs b/tests/test_std.rs
index e1bd8cbbc..de8d660f0 100644
--- a/tests/test_std.rs
+++ b/tests/test_std.rs
@@ -83,6 +83,14 @@ fn interleave_shortest() {
     let i1 = ::std::iter::repeat(1);
     let it = v0.into_iter().interleave_shortest(i1);
     assert_eq!(it.size_hint(), (6, Some(6)));
+
+    // Issue #1068: combined lower bound used to overflow when both halves
+    // reported saturating lower bounds, panicking in debug builds.
+    let i0 = ::std::iter::repeat(0).take(usize::MAX);
+    let i1 = ::std::iter::repeat(1);
+    let it = i0.interleave_shortest(i1);
+    let (lower, _) = it.size_hint();
+    assert_eq!(lower, usize::MAX);
 }
 
 #[test]