diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index 254fbc72a8c7e..8d4c58345f7b6 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -1932,6 +1932,11 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
                 }
             }
         }
+
+        // Some UI tests trigger behavior in rustc where it reads $CARGO and changes behavior if it exists.
+        // To make the tests work that rely on it not being set, make sure it is not set.
+        cmd.env_remove("CARGO");
+
         cmd.env("RUSTC_BOOTSTRAP", "1");
         // Override the rustc version used in symbol hashes to reduce the amount of normalization
         // needed when diffing test output.