diff --git a/compiler/rustc_resolve/src/diagnostics/impls.rs b/compiler/rustc_resolve/src/diagnostics/impls.rs
index 0b6b9899f48a6..b4a22a545f04f 100644
--- a/compiler/rustc_resolve/src/diagnostics/impls.rs
+++ b/compiler/rustc_resolve/src/diagnostics/impls.rs
@@ -3667,7 +3667,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     /// Gets the `#[diagnostic::on_unknown]` attribute data associated with this `DefId`.
-    fn on_unknown_data(&self, def_id: DefId) -> Option<&Directive> {
+    pub(crate) fn on_unknown_data(&self, def_id: DefId) -> Option<&Directive> {
         match def_id.as_local() {
             Some(local) => Some(self.on_unknown_data.get(&local)?.directive.as_ref()),
             None => find_attr!(self.tcx, def_id, OnUnknown{ directive } => directive)?.as_deref(),
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index 5260f724385f8..e26bfa6b96d51 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -19,6 +19,7 @@ use rustc_errors::{
     struct_span_code_err,
 };
 use rustc_hir as hir;
+use rustc_hir::attrs::diagnostic::{CustomDiagnostic, FormatArgs};
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{CtorKind, CtorOf, DefKind, MacroKinds};
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId};
@@ -163,6 +164,7 @@ struct BaseError {
     could_be_expr: bool,
     suggestion: Option<(Span, &'static str, String)>,
     module: Option<DefId>,
+    notes: Vec<String>,
 }
 
 #[derive(Debug)]
@@ -388,7 +390,6 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         // Make the base error.
         let mut expected = source.descr_expected();
         let path_str = Segment::names_to_string(path);
-        let item_str = path.last().unwrap().ident;
 
         if let Some(res) = res {
             BaseError {
@@ -404,12 +405,13 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 could_be_expr,
                 suggestion: None,
                 module: None,
+                notes: Vec::new(),
             }
         } else {
             let mut span_label = None;
             let item_ident = path.last().unwrap().ident;
             let item_span = item_ident.span;
-            let (mod_prefix, mod_str, module, suggestion) = if path.len() == 1 {
+            let (tick, mod_prefix, mod_str, module, suggestion) = if path.len() == 1 {
                 debug!(?self.diag_metadata.current_impl_items);
                 debug!(?self.diag_metadata.current_function);
                 let suggestion = if self.current_trait_ref.is_none()
@@ -420,7 +422,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     && let Some(item) = items.iter().find(|i| {
                         i.kind.ident().is_some_and(|ident| {
                             // Don't suggest if the item is in Fn signature arguments (#112590).
-                            ident.name == item_str.name && !sig.span.contains(item_span)
+                            ident.name == item_ident.name && !sig.span.contains(item_span)
                         })
                     }) {
                     let sp = item_span.shrink_to_lo();
@@ -490,15 +492,16 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 } else {
                     None
                 };
-                (String::new(), "this scope".to_string(), None, suggestion)
+                ("", String::new(), "this scope".to_string(), None, suggestion)
             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
                 if self.r.tcx.sess.edition() > Edition::Edition2015 {
                     // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
                     // which overrides all other expectations of item type
                     expected = "crate";
-                    (String::new(), "the list of imported crates".to_string(), None, None)
+                    ("", String::new(), "the list of imported crates".to_string(), None, None)
                 } else {
                     (
+                        "",
                         String::new(),
                         "the crate root".to_string(),
                         Some(CRATE_DEF_ID.to_def_id()),
@@ -506,7 +509,13 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     )
                 }
             } else if path.len() == 2 && path[0].ident.name == kw::Crate {
-                (String::new(), "the crate root".to_string(), Some(CRATE_DEF_ID.to_def_id()), None)
+                (
+                    "",
+                    String::new(),
+                    "the crate root".to_string(),
+                    Some(CRATE_DEF_ID.to_def_id()),
+                    None,
+                )
             } else {
                 let mod_path = &path[..path.len() - 1];
                 let mod_res = self.resolve_path(mod_path, Some(TypeNS), None, source);
@@ -519,41 +528,66 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
                 let mod_prefix =
                     mod_prefix.map_or_else(String::new, |res| format!("{} ", res.descr()));
-                (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)), module_did, None)
+                ("`", mod_prefix, Segment::names_to_string(mod_path), module_did, None)
             };
 
-            let (fallback_label, suggestion) = if path_str == "async"
-                && expected.starts_with("struct")
-            {
-                ("`async` blocks are only allowed in Rust 2018 or later".to_string(), suggestion)
+            let suggestion =
+                if ["true", "false"].contains(&item_ident.to_string().to_lowercase().as_str()) {
+                    // check if we are in situation of typo like `True` instead of `true`.
+                    let item_typo = item_ident.to_string().to_lowercase();
+                    Some((item_span, "you may want to use a bool value instead", item_typo))
+                // FIXME(vincenzopalazzo): make the check smarter,
+                // and maybe expand with levenshtein distance checks
+                } else if item_ident.as_str() == "printf" {
+                    Some((
+                        item_span,
+                        "you may have meant to use the `print` macro",
+                        "print!".to_owned(),
+                    ))
+                } else {
+                    suggestion
+                };
+            let mut msg = format!(
+                "cannot find {expected} `{item_ident}` in {mod_prefix}{tick}{mod_str}{tick}"
+            );
+            let mut fallback_label = if path_str == "async" && expected.starts_with("struct") {
+                "`async` blocks are only allowed in Rust 2018 or later".to_string()
             } else {
-                // check if we are in situation of typo like `True` instead of `true`.
-                let override_suggestion =
-                    if ["true", "false"].contains(&item_str.to_string().to_lowercase().as_str()) {
-                        let item_typo = item_str.to_string().to_lowercase();
-                        Some((item_span, "you may want to use a bool value instead", item_typo))
-                    // FIXME(vincenzopalazzo): make the check smarter,
-                    // and maybe expand with levenshtein distance checks
-                    } else if item_str.as_str() == "printf" {
-                        Some((
-                            item_span,
-                            "you may have meant to use the `print` macro",
-                            "print!".to_owned(),
-                        ))
-                    } else {
-                        suggestion
-                    };
-                (format!("not found in {mod_str}"), override_suggestion)
+                format!("not found in {tick}{mod_str}{tick}")
             };
+            let mut notes = Vec::new();
+            if let Some(module_def_id) = module
+                && let Some(directive) = self.r.on_unknown_data(module_def_id)
+            {
+                let args = FormatArgs { unresolved: item_ident.to_string(), this: mod_str, .. };
+                let CustomDiagnostic {
+                    message,
+                    label,
+                    notes: custom_notes,
+                    parent_label: _unreachable,
+                } = directive.eval(None, &args);
+                if let Some(message) = message {
+                    notes.push(msg);
+                    msg = message;
+                }
+                if let Some(label) = label {
+                    fallback_label = label;
+                    if let Some((_, span_label)) = span_label.take() {
+                        notes.push(span_label.to_string());
+                    }
+                }
+                notes.extend(custom_notes);
+            }
 
             BaseError {
-                msg: format!("cannot find {expected} `{item_str}` in {mod_prefix}{mod_str}"),
+                msg,
                 fallback_label,
                 span: item_span,
                 span_label,
                 could_be_expr,
                 suggestion,
                 module,
+                notes,
             }
         }
     }
@@ -679,6 +713,9 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         if let Some((span, label)) = base_error.span_label {
             err.span_label(span, label);
         }
+        for note in &base_error.notes {
+            err.note(note.clone());
+        }
 
         if let Some(ref sugg) = base_error.suggestion {
             err.span_suggestion_verbose(sugg.0, sugg.1, &sugg.2, Applicability::MaybeIncorrect);
diff --git a/tests/ui/diagnostic_namespace/on_unknown/late_res.rs b/tests/ui/diagnostic_namespace/on_unknown/late_res.rs
new file mode 100644
index 0000000000000..e549cb97b9d3a
--- /dev/null
+++ b/tests/ui/diagnostic_namespace/on_unknown/late_res.rs
@@ -0,0 +1,27 @@
+#![crate_type = "lib"]
+#![feature(diagnostic_on_unknown)]
+
+#[diagnostic::on_unknown(
+    message = "it works `{This}` `{Unresolved}`",
+    label = "label it works",
+    note = "note it works"
+)]
+pub mod empty {}
+
+fn stuff(x: u32) {
+    match x {
+        empty::blah => {}
+        //~^ ERROR it works `empty` `blah` [E0531]
+        _ => {}
+    }
+
+    println!("{}", empty::blah);
+    //~^ ERROR it works `empty` `blah` [E0425]
+
+    let x = [
+        empty::blah,
+        //~^ ERROR it works `empty` `blah` [E0425]
+        empty::blah2,
+        //~^ ERROR it works `empty` `blah2` [E0425]
+    ];
+}
diff --git a/tests/ui/diagnostic_namespace/on_unknown/late_res.stderr b/tests/ui/diagnostic_namespace/on_unknown/late_res.stderr
new file mode 100644
index 0000000000000..e2bb621814d47
--- /dev/null
+++ b/tests/ui/diagnostic_namespace/on_unknown/late_res.stderr
@@ -0,0 +1,40 @@
+error[E0531]: it works `empty` `blah`
+  --> $DIR/late_res.rs:13:16
+   |
+LL |         empty::blah => {}
+   |                ^^^^ label it works
+   |
+   = note: cannot find unit struct, unit variant or constant `blah` in module `empty`
+   = note: note it works
+
+error[E0425]: it works `empty` `blah`
+  --> $DIR/late_res.rs:18:27
+   |
+LL |     println!("{}", empty::blah);
+   |                           ^^^^ label it works
+   |
+   = note: cannot find value `blah` in module `empty`
+   = note: note it works
+
+error[E0425]: it works `empty` `blah`
+  --> $DIR/late_res.rs:22:16
+   |
+LL |         empty::blah,
+   |                ^^^^ label it works
+   |
+   = note: cannot find value `blah` in module `empty`
+   = note: note it works
+
+error[E0425]: it works `empty` `blah2`
+  --> $DIR/late_res.rs:24:16
+   |
+LL |         empty::blah2,
+   |                ^^^^^ label it works
+   |
+   = note: cannot find value `blah2` in module `empty`
+   = note: note it works
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0425, E0531.
+For more information about an error, try `rustc --explain E0425`.