diff --git a/releasenotes.md b/releasenotes.md
index 32218ec19..105816245 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -6,6 +6,7 @@
 
 ### Fixes
 - Bug in `io::write_using_write_byte`.
+- Bitstruct value cannot be used to index a const array in compile time. #2512
 
 ### Stdlib changes
 
diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index 6cad425b3..75c6c5f38 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -3855,7 +3855,7 @@ static inline bool sema_expr_resolve_subscript_index(SemaContext *context, Expr
 	}
 	else
 	{
-		if (!sema_analyse_expr(context, index))
+		if (!sema_analyse_expr_rvalue(context, index))
 		{
 			expr_poison(index);
 			return false;
@@ -3875,7 +3875,7 @@ static inline bool sema_expr_resolve_subscript_index(SemaContext *context, Expr
 	ArrayIndex size;
 	bool check_len = !context->call_env.in_no_eval || current_type == type_untypedlist;
 	Expr *len_expr = current_expr->expr_kind == EXPR_CT_IDENT ? current_expr->ct_ident_expr.decl->var.init_expr : current_expr;
-	if (expr_is_const_int(index) && (size = sema_len_from_expr(len_expr)) >= 0)
+	if (sema_cast_const(index)&& expr_is_const_int(index) && (size = sema_len_from_expr(len_expr)) >= 0)
 	{
 		// 4c. And that it's in range.
 		if (int_is_neg(index->const_expr.ixx))
diff --git a/test/test_suite/bitstruct/bitstruct_to_index.c3t b/test/test_suite/bitstruct/bitstruct_to_index.c3t
new file mode 100644
index 000000000..844993520
--- /dev/null
+++ b/test/test_suite/bitstruct/bitstruct_to_index.c3t
@@ -0,0 +1,25 @@
+// #target: macos-x64
+module test;
+import std;
+
+bitstruct Some : char
+{
+	char v : 0 .. 4;
+}
+
+const int[8] SOME_MAP = some_macro();
+
+macro some_macro()
+{
+	Some $s = { 8 };
+	int[8] $map;
+	$for var $i = 0; $i < 4; $i++:
+		$s = { .v = $s.v >> 1 };
+		$map[$s.v] = 1;
+	$endfor;
+	return $map;
+}
+
+/* #expect: test.ll
+
+@test.SOME_MAP = local_unnamed_addr constant { i32, i32, i32, i32, i32, [3 x i32] } { i32 1, i32 1, i32 1, i32 0, i32 1, [3 x i32] zeroinitializer }, align 16