diff --git a/test/test_acceptance.ml b/test/test_acceptance.ml
index 5455c9e..bd6be1b 100644
--- a/test/test_acceptance.ml
+++ b/test/test_acceptance.ml
@@ -3105,11 +3105,12 @@ ERR@7 unexpected token: not the kind the caller was reading
     else print_endline "acceptance: the DWARF verifier cases skipped (no opt)";
 
     (* A debug build and a release build must still be the same program. *)
-    let debug_compile ?(dev = false) path =
+    let debug_compile ?(dev = false) ?(x86 = false) path =
       let exe =
         Filename.concat scratch
           ("flan-dbg-" ^ Filename.remove_extension (Filename.basename path)
-           ^ if dev then "-dev" else "")
+           ^ (if dev then "-dev" else "")
+           ^ if x86 then "-x86" else "")
       in
       let l = Load.program ~file:path (Reader.read_file path) in
       let p = Check.program l.Load.decls in
@@ -3125,7 +3126,7 @@ ERR@7 unexpected token: not the kind the caller was reading
       in
       let p, csrcs, lflags = Reach.link ~dev l p in
       ignore
-        (Build.executable ~opts:{ Build.default with debug = true; dev }
+        (Build.executable ~opts:{ Build.default with debug = true; dev; x86 }
            ~csrcs ~lflags ~pnames p ~out:exe);
       exe
     in
@@ -3258,7 +3259,47 @@ ERR@7 unexpected token: not the kind the caller was reading
                n;
              print_endline text
            end)
-        [ "flan.tick"; "flan.main at debug.flan:" ]
+        [ "flan.tick"; "flan.main at debug.flan:" ];
+
+      (* And the same program through the hand-written x86-64 backend, which
+         emits its own DWARF rather than handing LLVM metadata.
+
+         The claim is narrower than the one above and deliberately so: a
+         breakpoint resolved on a Flan name, and a backtrace whose frames name
+         a .flan file and a line. No [frame variable], because [x86.ml] emits
+         no [DW_TAG_variable] -- a slot there is a bump-allocated frame
+         temporary whose lifetime the backend does not model, and a name
+         attached to an offset something else reuses would be a lie. That is
+         the gap between the two backends and this is where it is recorded.
+
+         Worth pinning rather than leaving to a handoff's transcript, because
+         everything this exercises is bytes [x86.ml] wrote by hand -- a line
+         program, a compile unit and an abbreviation table -- and a wrong byte
+         in any of them is silent. The program still printing the same four
+         lines is checked too, since debug information that breaks the build
+         it describes has helped nobody. *)
+      let exe = debug_compile ~x86:true "programs/debug.flan" in
+      let code, text = run exe None in
+      if text <> expected || code <> 0 then begin
+        incr failures;
+        Printf.printf
+          "FAIL  an --x86 --debug build of debug.flan runs the same\n\
+           \        got: %S (exit %d)\n     wanted: %S\n"
+          text code expected
+      end;
+      let _, text =
+        lldb_run exe [ "breakpoint set --name flan.tick"; "run"; "bt" ]
+      in
+      List.iter
+        (fun n ->
+           if not (contains text n) then begin
+             incr failures;
+             Printf.printf
+               "FAIL  lldb: --x86 --debug names Flan files and lines\n\
+                \        wanted %S\n" n;
+             print_endline text
+           end)
+        [ "flan.tick"; "at debug.flan:"; "flan.main at debug.flan:" ]
     end
     else print_endline "acceptance: lldb cases skipped (no lldb on PATH)";