Hi café, I observe that rewrite rules from imported modules are ignored by GHC. Given these two files, one module and one executable, the problem can be demonstrated by switching between `rewrite_me` and `rewrite_me_local`. If the rule fires, the program should run cleanly, as the `error` term should be rewritten to `()`. The imported function rewrite_me is not rewritten; but the same thing, rewrite_me_local, defined in the same program, will be rewritten. File RuleModule.hs module RuleModule where {-# NOINLINE rewrite_me #-} rewrite_me :: () -> () rewrite_me = error "Should rewrite" {-# RULES "rewrite_me" forall input . rewrite_me input = () #-} File Rule.hs import RuleModule {-# NOINLINE rewrite_me_local #-} rewrite_me_local :: () -> () rewrite_me_local = error "Should rewrite" {-# RULES "rewrite_local" forall input . rewrite_me_local input = () #-} -- Replace with rewrite_me_local and it's all good. main = case rewrite_me () of () -> return () This is GHC 7.10.2. I compile using -O -fenable-rewrite-rules. Using -dverbose-core2core, the "Desugar (after optimization)" section shows no rules when using rewrite_me, but shows the rule rewrite_local when using the local variant. Maybe this is expected, but I thought it important to mention. Thanks for any advice, Alex