fix

vlib/v/checker/fn.v

@@ -1712,13 +1712,17 @@ fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 				for i, mut arg in node.args {
 					targ := c.check_expr_opt_call(arg.expr, c.expr(arg.expr))
 					arg.typ = targ
-					earg_types << targ
 
 					param := if info.func.is_variadic && i >= info.func.params.len - 1 {
 						info.func.params.last()
 					} else {
 						info.func.params[i]
 					}
+					if c.table.sym(param.typ).kind == .interface_ {
+						earg_types << param.typ
+					} else {
+						earg_types << targ
+					}
 					param_share := param.typ.share()
 					if param_share == .shared_t
 						&& (c.locked_names.len > 0 || c.rlocked_names.len > 0) {

vlib/v/tests/iface_arg_test.v

@@ -0,0 +1,28 @@
+interface ITest {
+}
+
+struct Test {
+}
+
+struct Cmdable {
+mut:
+	call fn (cmd ITest)
+}
+
+fn (t Test) test(a ITest) {}
+
+fn test(a ITest) {}
+
+fn get() Test {
+	return Test{}
+}
+
+fn test_main() {
+	mut a := Cmdable{}
+	a.call = test
+	a.call(Test{})
+	test(Test{})
+	Test{}.test(a)
+
+	assert true
+}