diff --git a/compiler/add_pragma_decl.m b/compiler/add_pragma_decl.m
index f2219e358..fc308262c 100644
--- a/compiler/add_pragma_decl.m
+++ b/compiler/add_pragma_decl.m
@@ -154,9 +154,8 @@ add_decl_pragmas_type_spec([Pragma | Pragmas], !ModuleInfo, !QualInfo,
 add_decl_pragmas_input_mode_spec([], !ModuleInfo, !ErrSpecsWarnSpecs).
 add_decl_pragmas_input_mode_spec([ImsList | ImsLists],
         !ModuleInfo, !ErrSpecs) :-
-    ImsList = ims_sub_list(ItemMercuryStatus, Pragmas),
-    list.foldl2(add_pragma_input_mode_spec(ItemMercuryStatus), Pragmas,
-        !ModuleInfo, !ErrSpecs),
+    ImsList = ims_sub_list(_ItemMercuryStatus, Pragmas),
+    list.foldl2(add_pragma_input_mode_spec, Pragmas, !ModuleInfo, !ErrSpecs),
     add_decl_pragmas_input_mode_spec(ImsLists, !ModuleInfo, !ErrSpecs).
 
 add_decl_pragmas_termination([], !ModuleInfo, !ErrSpecs).
@@ -212,8 +211,7 @@ add_decl_pragma(ProgressStream, ItemMercuryStatus, Pragma,
             !ErrSpecs, !WarnSpecs)
     ;
         Pragma = decl_pragma_input_mode_spec(InputSpecInfo),
-        add_pragma_input_mode_spec(ItemMercuryStatus, InputSpecInfo,
-            !ModuleInfo, !ErrSpecs)
+        add_pragma_input_mode_spec(InputSpecInfo, !ModuleInfo, !ErrSpecs)
     ;
         Pragma = decl_pragma_oisu(OISUInfo),
         add_pragma_oisu(OISUInfo, ItemMercuryStatus, !ModuleInfo, !ErrSpecs)
@@ -393,12 +391,11 @@ mark_pred_as_format_call(FormatCallInfo, PragmaStatus, !ModuleInfo,
 
 %---------------------%
 
-:- pred add_pragma_input_mode_spec(item_mercury_status::in,
-    decl_pragma_input_mode_spec_info::in, module_info::in, module_info::out,
+:- pred add_pragma_input_mode_spec(decl_pragma_input_mode_spec_info::in,
+    module_info::in, module_info::out,
     list(err_spec)::in, list(err_spec)::out) is det.
 
-add_pragma_input_mode_spec(ItemMercuryStatus, InputSpec,
-        !ModuleInfo, !ErrSpecs) :-
+add_pragma_input_mode_spec(InputSpec, !ModuleInfo, !ErrSpecs) :-
     % XXX If we ever want to get smart recompilation working, we may
     % have to do something with _RecompIds. What we do for type_spec pragmas
     % may, or may not, be appropriate for input spec pragmas as well.
@@ -407,35 +404,6 @@ add_pragma_input_mode_spec(ItemMercuryStatus, InputSpec,
         TVarSet, Context, _),
     some [!InputSpecs] (
         !:InputSpecs = [],
-        (
-            ItemMercuryStatus = item_defined_in_other_module(_)
-        ;
-            ItemMercuryStatus = item_defined_in_this_module(ItemExport),
-            (
-                ItemExport = item_export_anywhere,
-                (
-                    ReplaceOrAdd = replace_in_mode,
-                    StatusPieces = [words("Error: a"),
-                        pragma_decl("input_mode_spec"), words("declaration"),
-                        words("that occurs in the interface of its module"),
-                        words("is not allowed to specify")] ++
-                        color_as_incorrect([words("replace_in_mode,")]) ++
-                        [words("as this would contradict"),
-                        words("the mode declarations of the"),
-                        words("predicates and/or functions"),
-                        words("in its public interface."), nl],
-                    StatusSpec = spec($pred, severity_error, phase_pt2h,
-                        Context, StatusPieces),
-                    !:InputSpecs = [StatusSpec | !.InputSpecs]
-                ;
-                    ReplaceOrAdd = add_to_in_mode
-                )
-            ;
-                ( ItemExport = item_export_nowhere
-                ; ItemExport = item_export_only_submodules
-                )
-            )
-        ),
         module_info_get_type_table(!.ModuleInfo, TypeTable),
         check_input_mode_spec_type(TypeTable, Type,
             [], UnknownTypeCtors, [], NonDuTypeCtors, bag.init, TVars),
diff --git a/compiler/mercury_compile_front_end.m b/compiler/mercury_compile_front_end.m
index 53c328c8e..b5b92a4ab 100644
--- a/compiler/mercury_compile_front_end.m
+++ b/compiler/mercury_compile_front_end.m
@@ -1493,7 +1493,15 @@ simplify_pred(ProgressStream, SimplifyTasks0, PredId,
     ),
     PredSpecsAcc0 = init_diag_spec_accumulator,
     simplify_pred_procs(ProgressStream, SimplifyTasks, PredId, ProcIds,
-        !PredInfo, !ModuleInfo, PredSpecsAcc0, PredSpecsAcc),
+        [], InputSpecDeletePPIds, !PredInfo, !ModuleInfo,
+        PredSpecsAcc0, PredSpecsAcc),
+    AfterFrontEnd = SimplifyTasks ^ do_after_front_end,
+    (
+        AfterFrontEnd = not_after_front_end
+    ;
+        AfterFrontEnd = after_front_end,
+        list.foldl(delete_specified_proc, InputSpecDeletePPIds, !ModuleInfo)
+    ),
     PredSpecs = diag_spec_accumulator_to_list(PredSpecsAcc),
     !:Specs = PredSpecs ++ !.Specs,
     module_info_get_globals(!.ModuleInfo, Globals),
@@ -1502,6 +1510,16 @@ simplify_pred(ProgressStream, SimplifyTasks0, PredId,
         maybe_report_stats(ProgressStream, Statistics, !IO)
     ).
 
+:- pred delete_specified_proc(pred_proc_id::in,
+    module_info::in, module_info::out) is det.
+
+delete_specified_proc(proc(PredId, ProcId), !ModuleInfo) :-
+    module_info_pred_info(!.ModuleInfo, PredId, PredInfo0),
+    pred_info_get_proc_table(PredInfo0, ProcTable0),
+    map.delete(ProcId, ProcTable0, ProcTable),
+    pred_info_set_proc_table(ProcTable, PredInfo0, PredInfo),
+    module_info_set_pred_info(PredId, PredInfo, !ModuleInfo).
+
 %---------------------------------------------------------------------------%
 
 :- pred maybe_generate_style_warnings(io.text_output_stream::in,
diff --git a/compiler/options.m b/compiler/options.m
index 9b4e4f98e..9809c5fa5 100644
--- a/compiler/options.m
+++ b/compiler/options.m
@@ -5678,7 +5678,7 @@ optdb(oc_dev_ctrl,  compiler_sufficiently_recent,      bool(no),
         "scout-disj-2025-11-15",
         "subtype-int2-2026-08-09",
         "input-spec-2026-08-14",
-        "input-mode-spec-2026-08-31"], [
+        "input-mode-spec-2026-09-01"], [
         w("Is the compiler sufficiently recent to contain the new feature"),
         w("or bugfix referred to by each name?")])).
 % These options are provided for use by implementors who want to compare
diff --git a/compiler/simplify_proc.m b/compiler/simplify_proc.m
index e0fdce2c1..dab5ab653 100644
--- a/compiler/simplify_proc.m
+++ b/compiler/simplify_proc.m
@@ -44,6 +44,7 @@
     %
 :- pred simplify_pred_procs(io.text_output_stream::in,
     simplify_tasks::in, pred_id::in, list(proc_id)::in,
+    list(pred_proc_id)::in, list(pred_proc_id)::out,
     pred_info::in, pred_info::out, module_info::in, module_info::out,
     diag_spec_accumulator::in, diag_spec_accumulator::out) is det.
 
@@ -126,21 +127,22 @@
 
 %---------------------------------------------------------------------------%
 
-simplify_pred_procs(_, _, _, [], !PredInfo, !ModuleInfo, !Specs).
-simplify_pred_procs(ProgressStream, SimplifyTasks, PredId,
-        [ProcId | ProcIds], !PredInfo, !ModuleInfo, !Specs) :-
+simplify_pred_procs(_, _, _, [],
+        !InputSpecDeletePPIds, !PredInfo, !ModuleInfo, !Specs).
+simplify_pred_procs(ProgressStream, SimplifyTasks, PredId, [ProcId | ProcIds],
+        !InputSpecDeletePPIds, !PredInfo, !ModuleInfo, !Specs) :-
     simplify_pred_proc(ProgressStream, SimplifyTasks, PredId, ProcId,
-        !PredInfo, !ModuleInfo, !Specs),
+        !InputSpecDeletePPIds, !PredInfo, !ModuleInfo, !Specs),
     simplify_pred_procs(ProgressStream, SimplifyTasks, PredId, ProcIds,
-        !PredInfo, !ModuleInfo, !Specs).
+        !InputSpecDeletePPIds, !PredInfo, !ModuleInfo, !Specs).
 
 :- pred simplify_pred_proc(io.text_output_stream::in, simplify_tasks::in,
-    pred_id::in, proc_id::in, pred_info::in, pred_info::out,
-    module_info::in, module_info::out,
+    pred_id::in, proc_id::in, list(pred_proc_id)::in, list(pred_proc_id)::out,
+    pred_info::in, pred_info::out, module_info::in, module_info::out,
     diag_spec_accumulator::in, diag_spec_accumulator::out) is det.
 
 simplify_pred_proc(ProgressStream, SimplifyTasks, PredId, ProcId,
-        !PredInfo, !ModuleInfo, !Specs) :-
+        !InputSpecDeletePPIds, !PredInfo, !ModuleInfo, !Specs) :-
     % XXX It is strange that simplify_proc prints progress messages,
     % but simplify_pred_proc does not.
     pred_info_get_proc_table(!.PredInfo, ProcTable0),
@@ -166,6 +168,17 @@ simplify_pred_proc(ProgressStream, SimplifyTasks, PredId, ProcId,
     ;
         HasUserEvent = has_no_user_event
     ),
+    proc_info_get_maybe_input_spec(ProcInfo, MaybeInputSpec),
+    (
+        ( MaybeInputSpec = not_involved_in_input_spec
+        ; MaybeInputSpec = input_spec_original_proc_kept(_)
+        ; MaybeInputSpec = input_specialized_proc(_)
+        )
+    ;
+        MaybeInputSpec = input_spec_original_proc_logically_deleted(_),
+        PPId = proc(PredId, ProcId),
+        !:InputSpecDeletePPIds = [PPId | !.InputSpecDeletePPIds]
+    ),
     map.det_update(ProcId, ProcInfo, ProcTable0, ProcTable),
     pred_info_set_proc_table(ProcTable, !PredInfo),
     accumulate_diag_specs_for_proc(ProcSpecs, !Specs).
diff --git a/tests/warnings/help_text.err_exp b/tests/warnings/help_text.err_exp
index c0bc5e61f..db055fdc4 100644
--- a/tests/warnings/help_text.err_exp
+++ b/tests/warnings/help_text.err_exp
@@ -3730,7 +3730,7 @@ Options for developers only
     --scout-disj-2025-11-15
     --subtype-int2-2026-08-09
     --input-spec-2026-08-14
-    --input-mode-spec-2026-08-31
+    --input-mode-spec-2026-09-01
         Is the compiler sufficiently recent to contain the new feature or
         bugfix referred to by each name?