diff --git a/tests/script-based-pre/cargo_autoharness_fmt_impls/fmt-impls.sh b/tests/script-based-pre/cargo_autoharness_fmt_impls/fmt-impls.sh
index 65f949b65ad3..0e752169a126 100755
--- a/tests/script-based-pre/cargo_autoharness_fmt_impls/fmt-impls.sh
+++ b/tests/script-based-pre/cargo_autoharness_fmt_impls/fmt-impls.sh
@@ -2,4 +2,7 @@
 # Copyright Kani Contributors
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
-cargo kani autoharness -Z autoharness -Z function-contracts
+# Raise the harness timeout above autoharness's 60s default, like the other autoharness tests: on
+# the macOS x86_64 CI runners the `LowerExp`, `UpperExp` and `Pointer` harnesses take 40-60s and
+# often hit the default, which makes their expected failures time out instead.
+cargo kani autoharness -Z autoharness -Z function-contracts -Z unstable-options --harness-timeout 5m