diff --git a/vlib/v/checker/check_types.v b/vlib/v/checker/check_types.v
index 5e9da090e9..0ee6d63656 100644
--- a/vlib/v/checker/check_types.v
+++ b/vlib/v/checker/check_types.v
@@ -87,8 +87,8 @@ pub fn (mut c Checker) check_types(got ast.Type, expected ast.Type) bool {
 	}
 	if expected.has_flag(.optional) {
 		sym := c.table.sym(got)
-		if (sym.kind == .interface_ && sym.name == 'IError')
-			|| got in [ast.none_type, ast.error_type] {
+		if sym.idx == ast.error_type_idx || got in [ast.none_type, ast.error_type] {
+			// IErorr
 			return true
 		} else if !c.check_basic(got, expected.clear_flag(.optional)) {
 			return false
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 4a1716f917..75f99cf3cb 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1375,7 +1375,8 @@ fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos to
 			method := c.table.find_method_with_embeds(typ_sym, imethod.name) or {
 				// >> Hack to allow old style custom error implementations
 				// TODO: remove once deprecation period for `IError` methods has ended
-				if inter_sym.name == 'IError' && (imethod.name == 'msg' || imethod.name == 'code') {
+				if inter_sym.idx == ast.error_type_idx
+					&& (imethod.name == 'msg' || imethod.name == 'code') {
 					c.note("`$styp` doesn't implement method `$imethod.name` of interface `$inter_sym.name`. The usage of fields is being deprecated in favor of methods.",
 						pos)
 					continue
@@ -1421,7 +1422,8 @@ fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos to
 			if utyp != ast.voidptr_type {
 				// >> Hack to allow old style custom error implementations
 				// TODO: remove once deprecation period for `IError` methods has ended
-				if inter_sym.name == 'IError' && (ifield.name == 'msg' || ifield.name == 'code') {
+				if inter_sym.idx == ast.error_type_idx
+					&& (ifield.name == 'msg' || ifield.name == 'code') {
 					// do nothing, necessary warnings are already printed
 				} else {
 					// <<
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 25319f2dbb..21930b9784 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -2046,7 +2046,7 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 		g.write('.msg))')
 		return
 	}
-	if got_sym.kind == .none_ && exp_sym.name == 'IError' {
+	if got_sym.kind == .none_ && exp_sym.idx == ast.error_type_idx {
 		g.expr(expr)
 		return
 	}
@@ -5488,7 +5488,7 @@ static inline __shared__$interface_name ${shared_fn_name}(__shared__$cctype* x)
 			// >> Hack to allow old style custom error implementations
 			// TODO: remove once deprecation period for `IError` methods has ended
 			// fix MSVC not handling empty struct inits
-			if methods.len == 0 && interface_name == 'IError' {
+			if methods.len == 0 && isym.idx == ast.error_type_idx {
 				methods_struct.writeln('\t\t._method_msg = NULL,')
 				methods_struct.writeln('\t\t._method_code = NULL,')
 			}
diff --git a/vlib/v/gen/c/match.v b/vlib/v/gen/c/match.v
index bb07b2ce4e..37e4613f21 100644
--- a/vlib/v/gen/c/match.v
+++ b/vlib/v/gen/c/match.v
@@ -153,7 +153,8 @@ fn (mut g Gen) match_expr_sumtype(node ast.MatchExpr, is_expr bool, cond_var str
 						typ := branch.exprs[sumtype_index] as ast.TypeNode
 						branch_sym := g.table.sym(g.unwrap_generic(typ.typ))
 						g.write('${dot_or_ptr}_typ == _${sym.cname}_${branch_sym.cname}_index')
-					} else if branch.exprs[sumtype_index] is ast.None && sym.name == 'IError' {
+					} else if branch.exprs[sumtype_index] is ast.None
+						&& sym.idx == ast.error_type_idx {
 						g.write('${dot_or_ptr}_typ == _IError_None___index')
 					}
 				}