diff --git a/crates/perry/src/commands/compile/build_cache.rs b/crates/perry/src/commands/compile/build_cache.rs
index a7df4e805b..e91ddc739d 100644
--- a/crates/perry/src/commands/compile/build_cache.rs
+++ b/crates/perry/src/commands/compile/build_cache.rs
@@ -39,6 +39,13 @@ const BUILD_CACHE_ENV_VARS: &[&str] = &[
     "PERRY_WRITE_BARRIERS",
     "PERRY_SHADOW_STACK",
     "PERRY_RS4GC",
+    // #8128: the post-RS4GC `optnone`+`noinline` instruction cap. A function
+    // past the threshold has the middle-end skipped, so flipping this changes
+    // emitted code for that function — it must invalidate the build-level
+    // no-op check, not merely per-object entries. #8128 said it registered
+    // this and did not; `codegen_env_vars_are_build_cache_inputs` caught it on
+    // main, where it had gone red.
+    "PERRY_LL_RS4GC_OPTNONE_INSTRS",
     "PERRY_GC_SAFEPOINT_ONLY",
     "PERRY_INLINE_SHADOW_SLOT",
     "PERRY_DISABLE_BUFFER_FAST_PATH",