diff --git a/edb/edgeql/compiler/func.py b/edb/edgeql/compiler/func.py
index 1bb1294a60d..9041f22320b 100644
--- a/edb/edgeql/compiler/func.py
+++ b/edb/edgeql/compiler/func.py
@@ -41,6 +41,7 @@
 from edb.common.typeutils import not_none
 
 from edb.ir import ast as irast
+from edb.ir import staeval
 from edb.ir import utils as irutils
 
 from edb.schema import constraints as s_constr
@@ -1043,17 +1044,18 @@ def compile_fts_with_options(
     assert lang_ty
 
     lang_domain = set()  # languages that the fts index needs to support
-    if irutils.is_const(lang):
+    try:
+        lang_const = staeval.evaluate_to_python_val(lang, ctx.env.schema)
+    except staeval.UnsupportedExpressionError:
+        lang_const = None
+
+    if lang_const is not None:
         # language is constant
         # -> determine its only value at compile time
-        lang_const = irutils.as_const(lang)
-        assert lang_const
-        lang_domain.add(str(lang_const.value).lower())
-
+        lang_domain.add(lang_const.lower())
     else:
         # language is not constant
         # -> use all possible values of the enum
-
         enum_values = lang_ty.get_enum_values(ctx.env.schema)
         assert enum_values
         for enum_value in enum_values:
@@ -1061,17 +1063,14 @@ def compile_fts_with_options(
 
     # weight_category
     weight_expr = call.args['weight_category'].expr
-    if not irutils.is_const(weight_expr):
+    try:
+        weight: str = staeval.evaluate_to_python_val(
+            weight_expr, ctx.env.schema)
+    except staeval.UnsupportedExpressionError:
         raise errors.InvalidValueError(
             f"fts::search weight_category must be a constant",
             span=weight_expr.span,
-        )
-    weight_const = irutils.as_const(weight_expr)
-    if weight_const:
-        weight = str(weight_const.value)
-    else:
-        weight = None
-        assert weight
+        ) from None
 
     return irast.FTSDocument(
         text=call.args[0].expr,
diff --git a/edb/ir/utils.py b/edb/ir/utils.py
index 8e102821d7c..f253bd2fb8f 100644
--- a/edb/ir/utils.py
+++ b/edb/ir/utils.py
@@ -498,17 +498,6 @@ def flt(n: irast.Call) -> bool:
     return bool(ast.find_children(ir, irast.Call, flt, terminate_early=True))
 
 
-def as_const(ir: irast.Base) -> Optional[irast.BaseConstant]:
-    match ir:
-        case irast.BaseConstant():
-            return ir
-        case irast.TypeCast():
-            return as_const(ir.expr)
-        case irast.SetE() if ir.expr:
-            return as_const(ir.expr)
-    return None
-
-
 T = TypeVar('T')
 
 
diff --git a/tests/test_edgeql_fts_schema.py b/tests/test_edgeql_fts_schema.py
index b3dcf107004..38cb54b0dd4 100644
--- a/tests/test_edgeql_fts_schema.py
+++ b/tests/test_edgeql_fts_schema.py
@@ -555,3 +555,39 @@ async def test_edgeql_fts_schema_weight_03(self):
                 {"a": "hello world", "b": "running fox"},
             ],
         )
+
+    async def test_edgeql_fts_schema_fiddly_args_01(self):
+        await self.con.execute(
+            r'''
+            create type Doc {
+                create required property x -> str;
+                create index fts::index on (
+                    fts::with_options(
+                        .x,
+                        language := <fts::Language>('en'++'g'),
+                        weight_category := (select fts::Weight.B),
+                    )
+                );
+            };
+            '''
+        )
+
+    async def test_edgeql_fts_schema_fiddly_args_02(self):
+        async with self.assertRaisesRegexTx(
+            edgedb.InvalidValueError,
+            "fts::search weight_category must be a constant",
+        ):
+            await self.con.execute(
+                r'''
+                create type Doc {
+                    create required property x -> str;
+                    create index fts::index on (
+                        fts::with_options(
+                            .x,
+                            language := fts::Language.eng,
+                            weight_category := <fts::Weight>("AB"[0]),
+                         )
+                    );
+                };
+                '''
+            )