diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index eb60cad43e..2cc04f5f64 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -63,8 +63,15 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			}
 		}
 		if need_generic_names {
-			c.error('generic function declaration must specify generic type names, e.g. foo<T>',
-				node.pos)
+			if node.is_method {
+				c.add_error_detail('use `fn (r SomeType<T>) foo<T>() {`, not just `fn (r SomeType<T>) foo() {`')
+				c.error('generic method declaration must specify generic type names',
+					node.pos)
+			} else {
+				c.add_error_detail('use `fn foo<T>(x T) {`, not just `fn foo(x T) {`')
+				c.error('generic function declaration must specify generic type names',
+					node.pos)
+			}
 		}
 	}
 	if node.language == .v && !c.is_builtin_mod && !node.is_anon {
diff --git a/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.out b/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.out
index f94fd49448..4e5d935b9e 100644
--- a/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.out
+++ b/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.out
@@ -1,15 +1,24 @@
-vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:26:1: error: generic function declaration must specify generic type names, e.g. foo<T>
+vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:26:1: error: generic function declaration must specify generic type names
    24 | }
-   25 |
+   25 | 
    26 | fn g_worker(g Generic<T>) {
       | ~~~~~~~~~~~~~~~~~~~~~~~~~
    27 |     t := <-g.ch
    28 |     handle(t)
-vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:32:1: error: generic function declaration must specify generic type names, e.g. foo<T>
+Details: use `fn foo<T>(x T) {`, not just `fn foo(x T) {`
+vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:32:1: error: generic function declaration must specify generic type names
    30 | }
-   31 |
+   31 | 
    32 | fn handle(t T) {
       | ~~~~~~~~~~~~~~
-   33 |     println("hi")
+   33 |     println('hi')
    34 | }
-
+Details: use `fn foo<T>(x T) {`, not just `fn foo(x T) {`
+vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:40:1: error: generic method declaration must specify generic type names
+   38 | type MayBe<T> = None | T
+   39 | 
+   40 | fn (m MayBe<T>) is_some() bool {
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+   41 |     return m is T
+   42 | }
+Details: use `fn (r SomeType<T>) foo<T>() {`, not just `fn (r SomeType<T>) foo() {`
diff --git a/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv b/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv
index f455a3da05..e56bf3d6c7 100644
--- a/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv
+++ b/vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv
@@ -30,5 +30,13 @@ fn g_worker(g Generic<T>) {
 }
 
 fn handle(t T) {
-	println("hi")
+	println('hi')
+}
+
+struct None {}
+
+type MayBe<T> = None | T
+
+fn (m MayBe<T>) is_some() bool {
+	return m is T
 }