diff --git a/src/librustc_mir/build/matches/mod.rs b/src/librustc_mir/build/matches/mod.rs
index aa261f8eb6fb2..f23abf86bcfc8 100644
--- a/src/librustc_mir/build/matches/mod.rs
+++ b/src/librustc_mir/build/matches/mod.rs
@@ -142,7 +142,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // Step 2. Create the otherwise and prebinding blocks.
 
         // create binding start block for link them by false edges
-        let candidate_count = arms.iter().map(|c| c.patterns.len()).sum::<usize>();
+        let candidate_count = arms.iter().map(|c| c.top_pats_hack().len()).sum::<usize>();
         let pre_binding_blocks: Vec<_> = (0..candidate_count)
             .map(|_| self.cfg.start_new_block())
             .collect();
@@ -159,7 +159,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             .map(|arm| {
                 let arm_has_guard = arm.guard.is_some();
                 match_has_guard |= arm_has_guard;
-                let arm_candidates: Vec<_> = arm.patterns
+                let arm_candidates: Vec<_> = arm.top_pats_hack()
                     .iter()
                     .zip(candidate_pre_binding_blocks.by_ref())
                     .map(
@@ -238,7 +238,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let scope = this.declare_bindings(
                     None,
                     arm.span,
-                    &arm.patterns[0],
+                    &arm.top_pats_hack()[0],
                     ArmHasGuard(arm.guard.is_some()),
                     Some((Some(&scrutinee_place), scrutinee_span)),
                 );
diff --git a/src/librustc_mir/hair/cx/expr.rs b/src/librustc_mir/hair/cx/expr.rs
index f3d699fa4f008..bdfcacd0f4629 100644
--- a/src/librustc_mir/hair/cx/expr.rs
+++ b/src/librustc_mir/hair/cx/expr.rs
@@ -860,9 +860,9 @@ impl ToBorrowKind for hir::Mutability {
     }
 }
 
-fn convert_arm<'a, 'tcx>(cx: &mut Cx<'a, 'tcx>, arm: &'tcx hir::Arm) -> Arm<'tcx> {
+fn convert_arm<'tcx>(cx: &mut Cx<'_, 'tcx>, arm: &'tcx hir::Arm) -> Arm<'tcx> {
     Arm {
-        patterns: arm.top_pats_hack().iter().map(|p| cx.pattern_from_hir(p)).collect(),
+        pattern: cx.pattern_from_hir(&arm.pat),
         guard: match arm.guard {
                 Some(hir::Guard::If(ref e)) => Some(Guard::If(e.to_ref())),
                 _ => None,
diff --git a/src/librustc_mir/hair/mod.rs b/src/librustc_mir/hair/mod.rs
index 0638cb462f73b..63a9a83154b4f 100644
--- a/src/librustc_mir/hair/mod.rs
+++ b/src/librustc_mir/hair/mod.rs
@@ -293,7 +293,7 @@ pub struct FruInfo<'tcx> {
 
 #[derive(Clone, Debug)]
 pub struct Arm<'tcx> {
-    pub patterns: Vec<Pattern<'tcx>>,
+    pub pattern: Pattern<'tcx>,
     pub guard: Option<Guard<'tcx>>,
     pub body: ExprRef<'tcx>,
     pub lint_level: LintLevel,
@@ -301,6 +301,17 @@ pub struct Arm<'tcx> {
     pub span: Span,
 }
 
+impl Arm<'tcx> {
+    // HACK(or_patterns; Centril | dlrobertson): Remove this and
+    // correctly handle each case in which this method is used.
+    pub fn top_pats_hack(&self) -> &[Pattern<'tcx>] {
+        match &*self.pattern.kind {
+            PatternKind::Or { pats } => pats,
+            _ => std::slice::from_ref(&self.pattern),
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub enum Guard<'tcx> {
     If(ExprRef<'tcx>),