diff --git a/src/ir/lower/decl.zig b/src/ir/lower/decl.zig
index bc963f5..8457fb3 100644
--- a/src/ir/lower/decl.zig
+++ b/src/ir/lower/decl.zig
@@ -2247,13 +2247,28 @@ pub fn isVisible(self: *Lowering, name: []const u8, vis: resolver_mod.Visibility
         // this predicate is single-hop only.
         .impl_transitive => @panic("isVisible: transitive visibility is owned by findVisibleImpls"),
         .c_import_bare => {
-            // Foreign-C gate: only C-import fn_decls without a library_ref
-            // are policed; a non-foreign body or a library-bound foreign
-            // decl is unconditionally visible.
+            // Foreign-C gate: only a lib-less C-import fn_decl is policed; a
+            // library-bound decl (resolves via the named library, not a
+            // module edge) or a non-C body is unconditionally visible. The
+            // legacy `#foreign` form (a `foreign_expr` body) and the new
+            // `extern` keyword (`extern_export == .extern_`, empty-block body)
+            // are two spellings of the same lib-less C-symbol import, so BOTH
+            // route to `visibleOverEdges` here — a migrated `extern` decl must
+            // get the identical "C function not visible" diagnostic its
+            // `#foreign` twin did, not the generic top-level-name wording
+            // (FFI-linkage Part B; example 1228).
             const fd = self.program_index.fn_ast_map.get(name) orelse return true;
-            if (fd.body.data != .foreign_expr) return true;
-            if (fd.body.data.foreign_expr.library_ref != null) return true;
-            return self.visibleOverEdges(name);
+            switch (fd.body.data) {
+                .foreign_expr => |fe| {
+                    if (fe.library_ref != null) return true;
+                    return self.visibleOverEdges(name);
+                },
+                else => {
+                    if (fd.extern_export != .extern_) return true;
+                    if (fd.extern_lib != null) return true;
+                    return self.visibleOverEdges(name);
+                },
+            }
         },
         .user_bare_flat => return self.visibleOverEdges(name),
     }