diff --git a/src/expand.rs b/src/expand.rs
index 7c3ab5a..f868c7d 100644
--- a/src/expand.rs
+++ b/src/expand.rs
@@ -284,6 +284,13 @@
     };
 
     let mut outer_generics = generics.clone();
+    for p in &mut outer_generics.params {
+        match p {
+            GenericParam::Type(t) => t.default = None,
+            GenericParam::Const(c) => c.default = None,
+            GenericParam::Lifetime(_) => {}
+        }
+    }
     if !has_self {
         if let Some(mut where_clause) = outer_generics.where_clause {
             where_clause.predicates = where_clause
diff --git a/src/receiver.rs b/src/receiver.rs
index 1e9e397..4273359 100644
--- a/src/receiver.rs
+++ b/src/receiver.rs
@@ -29,6 +29,14 @@
     visitor.0
 }
 
+fn has_self_in_token_stream(tokens: TokenStream) -> bool {
+    tokens.into_iter().any(|tt| match tt {
+        TokenTree::Ident(ident) => ident == "Self",
+        TokenTree::Group(group) => has_self_in_token_stream(group.stream()),
+        _ => false,
+    })
+}
+
 struct HasSelf(bool);
 
 impl VisitMut for HasSelf {
@@ -54,6 +62,12 @@
     fn visit_item_mut(&mut self, _: &mut Item) {
         // Do not recurse into nested items.
     }
+
+    fn visit_macro_mut(&mut self, mac: &mut Macro) {
+        if !contains_fn(mac.tokens.clone()) {
+            self.0 |= has_self_in_token_stream(mac.tokens.clone());
+        }
+    }
 }
 
 pub struct ReplaceReceiver {
@@ -278,14 +292,14 @@
         }
     }
 
-    fn visit_macro_mut(&mut self, i: &mut Macro) {
+    fn visit_macro_mut(&mut self, mac: &mut Macro) {
         // We can't tell in general whether `self` inside a macro invocation
         // refers to the self in the argument list or a different self
         // introduced within the macro. Heuristic: if the macro input contains
         // `fn`, then `self` is more likely to refer to something other than the
         // outer function's self argument.
-        if !contains_fn(i.tokens.clone()) {
-            self.visit_token_stream(&mut i.tokens);
+        if !contains_fn(mac.tokens.clone()) {
+            self.visit_token_stream(&mut mac.tokens);
         }
     }
 }