diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 55ea12d25ea..902b4b1a1ec 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -1100,16 +1100,17 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                         replace_span: self.ending_semi_or_hi(item.span),
                         extern_block_suggestion: match sig.header.ext {
                             Extern::None => None,
-                            Extern::Implicit(start_span) => Some(ExternBlockSuggestion {
+                            Extern::Implicit(start_span) => Some(ExternBlockSuggestion::Implicit {
                                 start_span,
                                 end_span: item.span.shrink_to_hi(),
-                                abi: None,
-                            }),
-                            Extern::Explicit(abi, start_span) => Some(ExternBlockSuggestion {
-                                start_span,
-                                end_span: item.span.shrink_to_hi(),
-                                abi: Some(abi.symbol_unescaped),
                             }),
+                            Extern::Explicit(abi, start_span) => {
+                                Some(ExternBlockSuggestion::Explicit {
+                                    start_span,
+                                    end_span: item.span.shrink_to_hi(),
+                                    abi: abi.symbol_unescaped,
+                                })
+                            }
                         },
                     });
                 }
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 59f582f10d9..09e262452b1 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -1,6 +1,5 @@
 //! Errors emitted by ast_passes.
 
-use rustc_errors::{fluent, AddToDiagnostic, Applicability, Diagnostic, SubdiagnosticMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Span, Symbol};
 
@@ -207,28 +206,21 @@ pub struct FnWithoutBody {
     pub extern_block_suggestion: Option<ExternBlockSuggestion>,
 }
 
-pub struct ExternBlockSuggestion {
-    pub start_span: Span,
-    pub end_span: Span,
-    pub abi: Option<Symbol>,
-}
-
-impl AddToDiagnostic for ExternBlockSuggestion {
-    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
-    where
-        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
-    {
-        let start_suggestion = if let Some(abi) = self.abi {
-            format!("extern \"{}\" {{", abi)
-        } else {
-            "extern {".to_owned()
-        };
-        let end_suggestion = " }".to_owned();
-
-        diag.multipart_suggestion(
-            fluent::extern_block_suggestion,
-            vec![(self.start_span, start_suggestion), (self.end_span, end_suggestion)],
-            Applicability::MaybeIncorrect,
-        );
-    }
+#[derive(Subdiagnostic)]
+pub enum ExternBlockSuggestion {
+    #[multipart_suggestion(ast_passes_extern_block_suggestion, applicability = "maybe-incorrect")]
+    Implicit {
+        #[suggestion_part(code = "extern {{")]
+        start_span: Span,
+        #[suggestion_part(code = " }}")]
+        end_span: Span,
+    },
+    #[multipart_suggestion(ast_passes_extern_block_suggestion, applicability = "maybe-incorrect")]
+    Explicit {
+        #[suggestion_part(code = "extern \"{abi}\" {{")]
+        start_span: Span,
+        #[suggestion_part(code = " }}")]
+        end_span: Span,
+        abi: Symbol,
+    },
 }
diff --git a/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl b/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl
index e5cd1142b20..5f28839f136 100644
--- a/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl
@@ -88,4 +88,5 @@ ast_passes_ty_alias_without_body =
 ast_passes_fn_without_body =
     free function without a body
     .suggestion = provide a definition for the function
-    .extern_block_suggestion = if you meant to declare an externally defined function, use an `extern` block
+
+ast_passes_extern_block_suggestion = if you meant to declare an externally defined function, use an `extern` block