diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index cc378f1ea47c..ae2ab2b02521 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -265,6 +265,10 @@ impl<'tcx> AssociatedItems<'tcx> {
         self.items.iter().map(|(_, v)| *v)
     }
 
+    pub fn len(&self) -> usize {
+        self.items.len()
+    }
+
     /// Returns an iterator over all associated items with the given name, ignoring hygiene.
     pub fn filter_by_name_unhygienic(
         &self,
diff --git a/compiler/rustc_typeck/src/coherence/inherent_impls_overlap.rs b/compiler/rustc_typeck/src/coherence/inherent_impls_overlap.rs
index be77d049cae4..673cddbdb5f2 100644
--- a/compiler/rustc_typeck/src/coherence/inherent_impls_overlap.rs
+++ b/compiler/rustc_typeck/src/coherence/inherent_impls_overlap.rs
@@ -22,6 +22,14 @@ impl InherentOverlapChecker<'tcx> {
         let impl_items1 = self.tcx.associated_items(impl1);
         let impl_items2 = self.tcx.associated_items(impl2);
 
+        let mut impl_items1 = &impl_items1;
+        let mut impl_items2 = &impl_items2;
+
+        // Performance optimization: iterate over the smaller list
+        if impl_items1.len() > impl_items2.len() {
+            std::mem::swap(&mut impl_items1, &mut impl_items2);
+        }
+
         for item1 in impl_items1.in_definition_order() {
             let collision = impl_items2.filter_by_name_unhygienic(item1.ident.name).any(|item2| {
                 // Symbols and namespace match, compare hygienically.