diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index 4371f689a9cace..64f8c93c98d633 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -39,7 +39,7 @@ pub mut:
 	used_veb_types   []Type          // veb context types, filled in by checker
 	used_maps        int             // how many times maps were used, filled in by markused
 	used_arrays      int             // how many times arrays were used, filled in by markused
-	used_modules     map[string]bool // filled in checker
+	external_types   bool            // true, when external type is used
 	// json             bool            // json is imported
 	debugger       bool            // debugger is used
 	comptime_calls map[string]bool // resolved name to call on comptime
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 49ad605eacdf6e..b9ec682476a7e2 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -4004,7 +4004,7 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 				node.pos)
 		}
 		if c.pref.skip_unused && !c.is_builtin_mod && node.language == .v && node.name.contains('.') {
-			c.table.used_features.used_modules[node.name.all_before('.')] = true
+			c.table.used_features.external_types = true
 		}
 		if mut obj := node.scope.find(node.name) {
 			match mut obj {
diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 12cd03cd5e2fc2..16491e737c89eb 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -761,15 +761,14 @@ fn (mut c Checker) call_expr(mut node ast.CallExpr) ast.Type {
 		}
 	}
 	c.expected_or_type = old_expected_or_type
-	if c.pref.skip_unused && !c.is_builtin_mod && c.mod == 'main' {
+	if c.pref.skip_unused && !c.is_builtin_mod && c.mod == 'main'
+		&& !c.table.used_features.external_types {
 		if node.is_method {
-			type_str := c.table.type_to_str(node.left_type)
-			if c.table.sym(node.left_type).is_builtin()
-				&& type_str !in c.table.used_features.used_modules {
-				c.table.used_features.used_modules[type_str] = true
+			if c.table.sym(node.left_type).is_builtin() {
+				c.table.used_features.external_types = true
 			}
 		} else if node.name.contains('.') {
-			c.table.used_features.used_modules[node.name.all_before('.')] = true
+			c.table.used_features.external_types = true
 		}
 	}
 
diff --git a/vlib/v/checker/struct.v b/vlib/v/checker/struct.v
index 7028a6f516fa91..c6a52b575b5a4c 100644
--- a/vlib/v/checker/struct.v
+++ b/vlib/v/checker/struct.v
@@ -443,6 +443,10 @@ fn (mut c Checker) struct_init(mut node ast.StructInit, is_field_zero_struct_ini
 			node.typ = c.expected_type
 		}
 	}
+	if c.pref.skip_unused && !c.is_builtin_mod && !c.table.used_features.external_types {
+		type_str := c.table.type_to_str(node.typ)
+		c.table.used_features.external_types = type_str.contains('.') && type_str.len > 1
+	}
 	struct_sym := c.table.sym(node.typ)
 	mut old_inside_generic_struct_init := false
 	mut old_cur_struct_generic_types := []ast.Type{}
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 94c38ba25fbb9c..27ac7ec3ee12cd 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -6169,7 +6169,7 @@ fn (mut g Gen) write_init_function() {
 		g.write('\tas_cast_type_indexes = ')
 		g.writeln(g.as_cast_name_table())
 	}
-	if !g.pref.is_shared && (!g.pref.skip_unused || g.table.used_features.used_modules.len > 0) {
+	if !g.pref.is_shared && (!g.pref.skip_unused || g.table.used_features.external_types) {
 		// shared object does not need this
 		g.writeln('\tbuiltin_init();')
 	}
diff --git a/vlib/v/markused/markused.v b/vlib/v/markused/markused.v
index 515b41016ea922..779a997ede29c7 100644
--- a/vlib/v/markused/markused.v
+++ b/vlib/v/markused/markused.v
@@ -81,7 +81,7 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 			core_fns << ref_array_idx_str + '.push'
 			core_fns << ref_array_idx_str + '.pop'
 		}
-		if table.used_features.used_modules.len > 0 {
+		if table.used_features.external_types {
 			include_panic_deps = true
 		}
 		if pref_.autofree {
@@ -289,7 +289,7 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 			if table.used_features.auto_str || table.used_features.dump
 				|| table.used_features.print_types[mfn.receiver.typ.idx()]
 				|| table.used_features.asserts || table.used_features.debugger
-				|| table.used_features.used_modules.len > 0 {
+				|| table.used_features.external_types {
 				all_fn_root_names << k
 			}
 			continue
@@ -298,7 +298,7 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 			all_fn_root_names << k
 			continue
 		}
-		if (pref_.autofree || table.used_features.used_modules.len > 0) && k.ends_with('.free') {
+		if (pref_.autofree || table.used_features.external_types) && k.ends_with('.free') {
 			all_fn_root_names << k
 			continue
 		}
diff --git a/vlib/v/tests/skip_unused/ierror_str.run.out b/vlib/v/tests/skip_unused/ierror_str.run.out
new file mode 100644
index 00000000000000..88e9183d761a0c
--- /dev/null
+++ b/vlib/v/tests/skip_unused/ierror_str.run.out
@@ -0,0 +1 @@
+No such file or directory; code: 2
diff --git a/vlib/v/tests/skip_unused/ierror_str.skip_unused.run.out b/vlib/v/tests/skip_unused/ierror_str.skip_unused.run.out
new file mode 100644
index 00000000000000..88e9183d761a0c
--- /dev/null
+++ b/vlib/v/tests/skip_unused/ierror_str.skip_unused.run.out
@@ -0,0 +1 @@
+No such file or directory; code: 2
diff --git a/vlib/v/tests/skip_unused/ierror_str.vv b/vlib/v/tests/skip_unused/ierror_str.vv
new file mode 100644
index 00000000000000..38a3f03f42f7d0
--- /dev/null
+++ b/vlib/v/tests/skip_unused/ierror_str.vv
@@ -0,0 +1,6 @@
+import os
+
+fn main() {
+	mut proc := os.Process{}
+	proc.run()
+}