diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 9404040cf6f790..b02613e0942f77 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -3590,6 +3590,12 @@ fn (mut c Checker) method_call(mut node ast.CallExpr, mut continue_check &bool)
 		&& c.table.register_fn_concrete_types(method.fkey(), concrete_types) {
 		c.need_recheck_generic_fns = true
 	}
+	if method_name == 'str' && c.table.cur_fn != unsafe { nil } && c.table.cur_fn.is_method
+		&& c.table.cur_fn.name == 'str' && node.left is ast.Ident
+		&& (node.left as ast.Ident).name == c.table.cur_fn.receiver.name
+		&& left_type.idx() == c.table.cur_fn.receiver.typ.idx() {
+		c.error('cannot call `str()` method recursively', node.pos)
+	}
 	node.is_noreturn = method.is_noreturn
 	node.is_expand_simple_interpolation = method.is_expand_simple_interpolation
 	node.is_ctor_new = method.is_ctor_new
diff --git a/vlib/v/checker/tests/sum_type_recursive_str_err.out b/vlib/v/checker/tests/sum_type_recursive_str_err.out
new file mode 100644
index 00000000000000..b622b8288c463c
--- /dev/null
+++ b/vlib/v/checker/tests/sum_type_recursive_str_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/sum_type_recursive_str_err.vv:6:12: error: cannot call `str()` method recursively
+    4 |     return match n {
+    5 |         u8 { n.str() }
+    6 |         else { n.str() }
+      |                  ~~~~~
+    7 |     }
+    8 | }
diff --git a/vlib/v/checker/tests/sum_type_recursive_str_err.vv b/vlib/v/checker/tests/sum_type_recursive_str_err.vv
new file mode 100644
index 00000000000000..918dec97fb94c0
--- /dev/null
+++ b/vlib/v/checker/tests/sum_type_recursive_str_err.vv
@@ -0,0 +1,12 @@
+type Num = u8 | u16
+
+fn (n Num) str() string {
+	return match n {
+		u8 { n.str() }
+		else { n.str() }
+	}
+}
+
+fn main() {
+	println(Num(u16(0)))
+}