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diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference.rs b/src/test/ui/borrowck/two-phase-reservation-sharing-interference.rs
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+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference.rs
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+// revisions: nll_target
+
+// The nll_beyond revision is disabled due to missing support from two-phase beyond autorefs
+//[nll_beyond]compile-flags: -Z two-phase-beyond-autoref
+//[nll_beyond]should-fail
+
+// This is a corner case that the current implementation is (probably)
+// treating more conservatively than is necessary. But it also does
+// not seem like a terribly important use case to cover.
+//
+// So this test is just making a note of the current behavior, with
+// the caveat that in the future, the rules may be loosened, at which
+// point this test might be thrown out.
+//
+// The convention for the listed revisions: "lxl" means lexical
+// lifetimes (which can be easier to reason about). "nll" means
+// non-lexical lifetimes. "nll_target" means the initial conservative
+// two-phase borrows that only applies to autoref-introduced borrows.
+// "nll_beyond" means the generalization of two-phase borrows to all
+// `&mut`-borrows (doing so makes it easier to write code for specific
+// corner cases).
+
+fn main() {
+    let mut vec = vec![0, 1];
+    let delay: &mut Vec<_>;
+    {
+        let shared = &vec;
+
+        // we reserve here, which could (on its own) be compatible
+        // with the shared borrow. But in the current implementation,
+        // its an error.
+        delay = &mut vec;
+        //[nll_beyond]~^  ERROR cannot borrow `vec` as mutable because it is also borrowed as immutable
+        //[nll_target]~^^ ERROR cannot borrow `vec` as mutable because it is also borrowed as immutable
+
+        shared[0];
+    }
+
+    // the &mut-borrow only becomes active way down here.
+    //
+    // (At least in theory; part of the reason this test fails is that
+    // the constructed MIR throws in extra &mut reborrows which
+    // flummoxes our attmpt to delay the activation point here.)
+    delay.push(2);
+}