diff --git a/src/Sema.zig b/src/Sema.zig
index 342213dad18e2035dbcb4a9c53312762ac4f3b38..81447d6361b23f947907881648e7412ac0de21d9 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -17030,14 +17030,14 @@ fn zirReify(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData, in
             const payload_val = union_val.val.optionalValue() orelse
                 return sema.addType(Type.initTag(.anyerror));
             const slice_val = payload_val.castTag(.slice).?.data;
-            const decl_index = slice_val.ptr.pointerDecl().?;
-            try sema.ensureDeclAnalyzed(decl_index);
-            const decl = mod.declPtr(decl_index);
-            const array_val: []Value = if (decl.val.castTag(.aggregate)) |some| some.data else &.{};
 
+            const len = try sema.usizeCast(block, src, slice_val.len.toUnsignedInt(mod.getTarget()));
             var names: Module.ErrorSet.NameMap = .{};
-            try names.ensureUnusedCapacity(sema.arena, array_val.len);
-            for (array_val) |elem_val| {
+            try names.ensureUnusedCapacity(sema.arena, len);
+            var i: usize = 0;
+            while (i < len) : (i += 1) {
+                var buf: Value.ElemValueBuffer = undefined;
+                const elem_val = slice_val.ptr.elemValueBuffer(mod, i, &buf);
                 const struct_val = elem_val.castTag(.aggregate).?.data;
                 // TODO use reflection instead of magic numbers here
                 // error_set: type,
@@ -17429,14 +17429,14 @@ fn zirReify(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData, in
             var buf: Value.ToTypeBuffer = undefined;
 
             const args_slice_val = args_val.castTag(.slice).?.data;
-            const args_decl_index = args_slice_val.ptr.pointerDecl().?;
-            try sema.ensureDeclAnalyzed(args_decl_index);
-            const args_decl = mod.declPtr(args_decl_index);
-            const args: []Value = if (args_decl.val.castTag(.aggregate)) |some| some.data else &.{};
-            var param_types = try sema.arena.alloc(Type, args.len);
-            var comptime_params = try sema.arena.alloc(bool, args.len);
+            const args_len = try sema.usizeCast(block, src, args_slice_val.len.toUnsignedInt(mod.getTarget()));
+            var param_types = try sema.arena.alloc(Type, args_len);
+            var comptime_params = try sema.arena.alloc(bool, args_len);
             var noalias_bits: u32 = 0;
-            for (args) |arg, i| {
+            var i: usize = 0;
+            while (i < args_len) : (i += 1) {
+                var arg_buf: Value.ElemValueBuffer = undefined;
+                const arg = args_slice_val.ptr.elemValueBuffer(mod, i, &arg_buf);
                 const arg_val = arg.castTag(.aggregate).?.data;
                 // TODO use reflection instead of magic numbers here
                 // is_generic: bool,
diff --git a/test/behavior.zig b/test/behavior.zig
index febd765d779c7da71f6d7c7198265090c9207d72..a4acb57124b9266cfb0a8d1a078c8c9465dc5f43 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -93,6 +93,7 @@ test {
     _ = @import("behavior/bugs/12794.zig");
     _ = @import("behavior/bugs/12801-1.zig");
     _ = @import("behavior/bugs/12801-2.zig");
+    _ = @import("behavior/bugs/12885.zig");
     _ = @import("behavior/bugs/12911.zig");
     _ = @import("behavior/bugs/12928.zig");
     _ = @import("behavior/byteswap.zig");
diff --git a/test/behavior/bugs/12885.zig b/test/behavior/bugs/12885.zig
new file mode 100644
index 0000000000000000000000000000000000000000..f1cc8f94b3e18f9c9e347696d03473f3746fe353
--- /dev/null
+++ b/test/behavior/bugs/12885.zig
@@ -0,0 +1,36 @@
+const std = @import("std");
+const builtin = std.builtin;
+const expect = std.testing.expect;
+
+const info = .{
+    .args = [_]builtin.Type.Error{
+        .{ .name = "bar" },
+    },
+};
+const Foo = @Type(.{
+    .ErrorSet = &info.args,
+});
+test "ErrorSet comptime_field_ptr" {
+    if (@import("builtin").zig_backend == .stage1) return error.SkipZigTest;
+
+    try expect(Foo == error{bar});
+}
+
+const fn_info = .{
+    .args = [_]builtin.Type.Fn.Param{
+        .{ .is_generic = false, .is_noalias = false, .arg_type = u8 },
+    },
+};
+const Bar = @Type(.{
+    .Fn = .{
+        .calling_convention = .Unspecified,
+        .alignment = 0,
+        .is_generic = false,
+        .is_var_args = false,
+        .return_type = void,
+        .args = &fn_info.args,
+    },
+});
+test "fn comptime_field_ptr" {
+    try expect(@typeInfo(Bar) == .Fn);
+}