diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index ca1705f26b540..a069c49b0cc1e 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -3216,7 +3216,7 @@ impl<'hir> OwnerNode<'hir> {
         }
     }
 
-    pub fn fn_decl(&self) -> Option<&FnDecl<'hir>> {
+    pub fn fn_decl(self) -> Option<&'hir FnDecl<'hir>> {
         match self {
             OwnerNode::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | OwnerNode::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
@@ -3400,19 +3400,20 @@ impl<'hir> Node<'hir> {
         }
     }
 
-    pub fn fn_decl(&self) -> Option<&'hir FnDecl<'hir>> {
+    pub fn fn_decl(self) -> Option<&'hir FnDecl<'hir>> {
         match self {
             Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
             | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig.decl),
-            Node::ForeignItem(ForeignItem { kind: ForeignItemKind::Fn(fn_decl, _, _), .. }) => {
+            Node::Expr(Expr { kind: ExprKind::Closure(Closure { fn_decl, .. }), .. })
+            | Node::ForeignItem(ForeignItem { kind: ForeignItemKind::Fn(fn_decl, _, _), .. }) => {
                 Some(fn_decl)
             }
             _ => None,
         }
     }
 
-    pub fn fn_sig(&self) -> Option<&'hir FnSig<'hir>> {
+    pub fn fn_sig(self) -> Option<&'hir FnSig<'hir>> {
         match self {
             Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
             | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 85642bf82ccc9..25c18cf50c11f 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -17,28 +17,6 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
 use rustc_target::spec::abi::Abi;
 
-fn fn_decl<'hir>(node: Node<'hir>) -> Option<&'hir FnDecl<'hir>> {
-    match node {
-        Node::Item(Item { kind: ItemKind::Fn(sig, _, _), .. })
-        | Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(sig, _), .. })
-        | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(sig, _), .. }) => Some(&sig.decl),
-        Node::Expr(Expr { kind: ExprKind::Closure(Closure { fn_decl, .. }), .. })
-        | Node::ForeignItem(ForeignItem { kind: ForeignItemKind::Fn(fn_decl, ..), .. }) => {
-            Some(fn_decl)
-        }
-        _ => None,
-    }
-}
-
-pub fn fn_sig<'hir>(node: Node<'hir>) -> Option<&'hir FnSig<'hir>> {
-    match &node {
-        Node::Item(Item { kind: ItemKind::Fn(sig, _, _), .. })
-        | Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(sig, _), .. })
-        | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(sig, _), .. }) => Some(sig),
-        _ => None,
-    }
-}
-
 #[inline]
 pub fn associated_body<'hir>(node: Node<'hir>) -> Option<BodyId> {
     match node {
@@ -389,7 +367,7 @@ impl<'hir> Map<'hir> {
 
     pub fn fn_decl_by_hir_id(self, hir_id: HirId) -> Option<&'hir FnDecl<'hir>> {
         if let Some(node) = self.find(hir_id) {
-            fn_decl(node)
+            node.fn_decl()
         } else {
             bug!("no node for hir_id `{}`", hir_id)
         }
@@ -397,7 +375,7 @@ impl<'hir> Map<'hir> {
 
     pub fn fn_sig_by_hir_id(self, hir_id: HirId) -> Option<&'hir FnSig<'hir>> {
         if let Some(node) = self.find(hir_id) {
-            fn_sig(node)
+            node.fn_sig()
         } else {
             bug!("no node for hir_id `{}`", hir_id)
         }
diff --git a/compiler/rustc_mir_transform/src/coverage/mod.rs b/compiler/rustc_mir_transform/src/coverage/mod.rs
index 2619626a5675f..e72d016d7ac91 100644
--- a/compiler/rustc_mir_transform/src/coverage/mod.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mod.rs
@@ -541,7 +541,7 @@ fn fn_sig_and_body<'tcx>(
     // to HIR for it.
     let hir_node = tcx.hir().get_if_local(def_id).expect("expected DefId is local");
     let fn_body_id = hir::map::associated_body(hir_node).expect("HIR node is a function with body");
-    (hir::map::fn_sig(hir_node), tcx.hir().body(fn_body_id))
+    (hir_node.fn_sig(), tcx.hir().body(fn_body_id))
 }
 
 fn get_body_span<'tcx>(
diff --git a/compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs b/compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs
index 99729391e02b0..f654d6e560c80 100644
--- a/compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs
+++ b/compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs
@@ -4,7 +4,6 @@ use rustc_errors::{
     MultiSpan,
 };
 use rustc_hir as hir;
-use rustc_middle::hir::map::fn_sig;
 use rustc_middle::ty::{self as ty, AssocItems, AssocKind, TyCtxt};
 use rustc_session::Session;
 use rustc_span::def_id::DefId;
@@ -368,7 +367,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
         &self,
         num_params_to_take: usize,
     ) -> String {
-        let fn_sig = self.tcx.hir().get_if_local(self.def_id).and_then(fn_sig);
+        let fn_sig = self.tcx.hir().get_if_local(self.def_id).and_then(hir::Node::fn_sig);
         let is_used_in_input = |def_id| {
             fn_sig.map_or(false, |fn_sig| {
                 fn_sig.decl.inputs.iter().any(|ty| match ty.kind {