diff --git a/Cargo.lock b/Cargo.lock
index 2d16515500878..b56b92217a1de 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4355,6 +4355,7 @@ version = "0.0.0"
 dependencies = [
  "fluent-bundle",
  "fluent-syntax",
+ "indexmap",
  "proc-macro2",
  "quote",
  "syn",
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 214d653d23c13..0598fbfad6e4d 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -641,7 +641,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // Unlike all the other GC helpers where we check if an `AllocId` is found in the interpreter or
         // is live, here all the IDs in the map are for dead allocations so we don't
         // need to check for liveness.
-        #[allow(rustc::potential_query_instability)] // Only used from Miri, not queries.
         self.memory.dead_alloc_map.retain(|id, _| reachable_allocs.contains(id));
     }
 }
diff --git a/compiler/rustc_macros/Cargo.toml b/compiler/rustc_macros/Cargo.toml
index f097aee54abb6..8f52685eb1975 100644
--- a/compiler/rustc_macros/Cargo.toml
+++ b/compiler/rustc_macros/Cargo.toml
@@ -10,6 +10,7 @@ proc-macro = true
 # tidy-alphabetical-start
 fluent-bundle = "0.16"
 fluent-syntax = "0.12"
+indexmap = "2.4.0"
 proc-macro2 = "1"
 quote = "1"
 syn = { version = "2.0.9", features = ["full"] }
diff --git a/compiler/rustc_macros/src/diagnostics/message.rs b/compiler/rustc_macros/src/diagnostics/message.rs
index 094736e94870b..63561e409b0ae 100644
--- a/compiler/rustc_macros/src/diagnostics/message.rs
+++ b/compiler/rustc_macros/src/diagnostics/message.rs
@@ -1,7 +1,8 @@
-use std::collections::{HashMap, HashSet};
+use std::collections::HashSet;
 
 use fluent_bundle::FluentResource;
 use fluent_syntax::ast::{Expression, InlineExpression, Pattern, PatternElement};
+use indexmap::IndexMap;
 use proc_macro2::{Span, TokenStream};
 use quote::quote;
 use syn::ext::IdentExt;
@@ -17,9 +18,6 @@ pub(crate) struct Message {
 }
 
 impl Message {
-    // About `allow(rustc::potential_query_instability)`: The order of key/values of `fields` and
-    // `field_map` doesn't matters.
-    #[allow(rustc::potential_query_instability)]
     pub(crate) fn new(
         attr_span: Span,
         message_span: Span,
@@ -36,8 +34,8 @@ impl Message {
             panic!("Did not parse into a message")
         };
 
-        let mut fields: HashMap<String, (&syn::Ident, bool)> =
-            HashMap::with_capacity(field_map.len());
+        let mut fields: IndexMap<String, (&syn::Ident, bool)> =
+            IndexMap::with_capacity(field_map.len());
         for (_, (ident, _)) in field_map {
             fields.insert(ident.unraw().to_string(), (ident, false));
         }
diff --git a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
index f9ef016a16af6..c99575ff7431d 100644
--- a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
+++ b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
@@ -92,8 +92,6 @@ impl SubdiagnosticDerive {
 
         let diag = &self.diag;
 
-        // FIXME(edition_2024): Fix the `keyword_idents_2024` lint to not trigger here?
-        #[allow(keyword_idents_2024)]
         let ret = structure.gen_impl(quote! {
             gen impl rustc_errors::Subdiagnostic for @Self {
                 fn add_to_diag<__G>(
diff --git a/compiler/rustc_macros/src/diagnostics/utils.rs b/compiler/rustc_macros/src/diagnostics/utils.rs
index b65e39469ec51..3cace48e3fb27 100644
--- a/compiler/rustc_macros/src/diagnostics/utils.rs
+++ b/compiler/rustc_macros/src/diagnostics/utils.rs
@@ -1,8 +1,9 @@
 use std::cell::RefCell;
-use std::collections::{BTreeSet, HashMap, HashSet};
+use std::collections::{BTreeSet, HashSet};
 use std::fmt;
 use std::str::FromStr;
 
+use indexmap::IndexMap;
 use proc_macro::Span;
 use proc_macro2::{Ident, TokenStream};
 use quote::{ToTokens, format_ident, quote};
@@ -260,7 +261,7 @@ impl<T> SetOnce<T> for SpannedOption<T> {
     }
 }
 
-pub(super) type FieldMap = HashMap<String, (syn::Ident, TokenStream)>;
+pub(super) type FieldMap = IndexMap<String, (syn::Ident, TokenStream)>;
 
 /// In the strings in the attributes supplied to this macro, we want callers to be able to
 /// reference fields in the format string. For example:
diff --git a/compiler/rustc_macros/src/lib.rs b/compiler/rustc_macros/src/lib.rs
index 8624e0524b04e..399f20ebfe1eb 100644
--- a/compiler/rustc_macros/src/lib.rs
+++ b/compiler/rustc_macros/src/lib.rs
@@ -1,5 +1,12 @@
 // tidy-alphabetical-start
-#![allow(rustc::default_hash_types)]
+#![allow(
+    rustc::default_hash_types,
+    reason = "we like performance but can't use `rustc_data_structures`"
+)]
+#![deny(
+    rustc::potential_query_instability,
+    reason = "macros shall produce deterministic output/errors"
+)]
 #![feature(never_type)]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_tracked_env)]
diff --git a/compiler/rustc_macros/src/print_attribute.rs b/compiler/rustc_macros/src/print_attribute.rs
index 0114e0dfde0db..132a98a98ee07 100644
--- a/compiler/rustc_macros/src/print_attribute.rs
+++ b/compiler/rustc_macros/src/print_attribute.rs
@@ -120,7 +120,6 @@ pub(crate) fn print_attribute(input: Structure<'_>) -> TokenStream {
         }
     };
 
-    #[allow(keyword_idents_2024)]
     input.gen_impl(quote! {
         #[allow(unused)]
         gen impl PrintAttribute for @Self {
diff --git a/compiler/rustc_macros/src/symbols.rs b/compiler/rustc_macros/src/symbols.rs
index 44cd63e57af4c..9ecd63caf4226 100644
--- a/compiler/rustc_macros/src/symbols.rs
+++ b/compiler/rustc_macros/src/symbols.rs
@@ -24,8 +24,7 @@
 //! CFG_RELEASE="0.0.0" cargo +nightly expand > /tmp/rustc_span.rs
 //! ```
 
-use std::collections::HashMap;
-
+use indexmap::IndexMap;
 use proc_macro2::{Span, TokenStream};
 use quote::quote;
 use syn::parse::{Parse, ParseStream, Result};
@@ -148,12 +147,12 @@ struct Predefined {
 }
 
 struct Entries {
-    map: HashMap<String, Predefined>,
+    map: IndexMap<String, Predefined>,
 }
 
 impl Entries {
     fn with_capacity(capacity: usize) -> Self {
-        Entries { map: HashMap::with_capacity(capacity) }
+        Entries { map: IndexMap::with_capacity(capacity) }
     }
 
     fn insert(&mut self, span: Span, s: &str, errors: &mut Errors) -> u32 {
diff --git a/compiler/rustc_pattern_analysis/src/lib.rs b/compiler/rustc_pattern_analysis/src/lib.rs
index 9e405c801867e..324ce0a4025e7 100644
--- a/compiler/rustc_pattern_analysis/src/lib.rs
+++ b/compiler/rustc_pattern_analysis/src/lib.rs
@@ -3,7 +3,7 @@
 //! [`rustc`] module.
 
 // tidy-alphabetical-start
-#![allow(unused_crate_dependencies)]
+#![cfg_attr(test, allow(unused_crate_dependencies))] // Used for integration tests, not unit tests
 // tidy-alphabetical-end
 
 pub(crate) mod checks;
diff --git a/compiler/rustc_session/src/config/sigpipe.rs b/compiler/rustc_session/src/config/sigpipe.rs
index 1830ee034855b..5777e82d65d0e 100644
--- a/compiler/rustc_session/src/config/sigpipe.rs
+++ b/compiler/rustc_session/src/config/sigpipe.rs
@@ -5,21 +5,17 @@
 ///
 /// Note that `SIG_IGN` has been the Rust default since 2014. See
 /// <https://github.com/rust-lang/rust/issues/62569>.
-#[allow(dead_code)]
 pub const DEFAULT: u8 = 0;
 
 /// Do not touch `SIGPIPE`. Use whatever the parent process uses.
-#[allow(dead_code)]
 pub const INHERIT: u8 = 1;
 
 /// Change `SIGPIPE` to `SIG_IGN` so that failed writes results in `EPIPE`
 /// that are eventually converted to `ErrorKind::BrokenPipe`.
-#[allow(dead_code)]
 pub const SIG_IGN: u8 = 2;
 
 /// Change `SIGPIPE` to `SIG_DFL` so that the process is killed when trying
 /// to write to a closed pipe. This is usually the desired behavior for CLI
 /// apps that produce textual output that you want to pipe to other programs
 /// such as `head -n 1`.
-#[allow(dead_code)]
 pub const SIG_DFL: u8 = 3;