diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index 8b0f3d702c1..8764444aa61 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -1786,7 +1786,10 @@ impl<'a> Builder<'a> {
             cargo.env("RUSTC_TLS_MODEL_INITIAL_EXEC", "1");
         }
 
-        if self.config.incremental {
+        // Ignore incremental modes except for stage0, since we're
+        // not guaranteeing correctness across builds if the compiler
+        // is changing under your feet.
+        if self.config.incremental && compiler.stage == 0 {
             cargo.env("CARGO_INCREMENTAL", "1");
         } else {
             // Don't rely on any default setting for incr. comp. in Cargo