diff --git a/lib/OptimizeMiniRust.ml b/lib/OptimizeMiniRust.ml
index 5d22de03..43162791 100644
--- a/lib/OptimizeMiniRust.ml
+++ b/lib/OptimizeMiniRust.ml
@@ -178,19 +178,7 @@ let rec infer_expr (env: env) infer_function (expected: typ) (known: known) (e:
       env, known, Let ({ b with mut = mut_var; typ = t1 }, e1, close a (Var 0) (lift 1 e2))
 
   | Call (Name n, targs, es) ->
-      let env, _ = infer_function env n in
-      if NameMap.mem n env.seen then
-        (* TODO: substitute targs in ts -- for now, we assume we don't have a type-polymorphic
-           function that gets instantiated with a reference type *)
-        let ts = NameMap.find n env.seen in
-        let (env, known), es = List.fold_left2 (fun ((env, known), es) e t ->
-            let env, known, e = infer_expr env infer_function t known e in
-            (env, known), e :: es
-          ) ((env, known), []) es ts
-        in
-        let es = List.rev es in
-        env, known, Call (Name n, targs, es)
-      else if n = ["lowstar";"ignore";"ignore"] then
+      if n = ["lowstar";"ignore";"ignore"] then
         (* Since we do not have type-level substitutions in MiniRust, we special-case ignore here.
            Ideally, it would be added to builtins with `Bound 0` as a suitable type for the
            argument. *)
@@ -199,18 +187,25 @@ let rec infer_expr (env: env) infer_function (expected: typ) (known: known) (e:
       else if n = ["Box"; "new"] then
         let env, known, e = infer_expr env infer_function (KList.one targs) known (KList.one es) in
         env, known, Call (Name n, targs, [ e ])
-      else if n = [ "lib"; "memzero0"; "memzero" ] then (
+      else if n = [ "lib"; "memzero0"; "memzero" ] then
         (* Same as ignore above *)
-        assert (List.length es = 2);
         let e1, e2 = KList.two es in
         let env, known, e1 = infer_expr env infer_function (Ref (None, Mut, Slice (KList.one targs))) known e1 in
         let env, known, e2 = infer_expr env infer_function u32 known e2 in
         env, known, Call (Name n, targs, [ e1; e2 ])
-      ) else (
-        KPrint.bprintf "[infer_expr-mut,call] uncaught issue with on %s\n" (String.concat " :: " n);
-        debug env;
-        failwith "FIXME"
-      )
+      else
+        (* Ensure this is visited *)
+        let env, _ = infer_function env n in
+        (* TODO: substitute targs in ts -- for now, we assume we don't have a type-polymorphic
+           function that gets instantiated with a reference type *)
+        let ts = NameMap.find n env.seen in
+        let (env, known), es = List.fold_left2 (fun ((env, known), es) e t ->
+            let env, known, e = infer_expr env infer_function t known e in
+            (env, known), e :: es
+          ) ((env, known), []) es ts
+        in
+        let es = List.rev es in
+        env, known, Call (Name n, targs, es)
 
   | Call (Operator o, [], _) ->
       (* Most operators are wrapping and were translated to a methodcall.