diff --git a/src/items.rs b/src/items.rs
index 116905187e5..99efbf9e0ca 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -645,8 +645,14 @@ impl<'a> FmtVisitor<'a> {
         let mut items: Vec<_> = itemize_list_with(self.config.struct_variant_width());
 
         // If one of the variants use multiple lines, use multi-lined formatting for all variants.
-        fn is_multi_line_variant(item: &ListItem) -> bool {
+        let is_multi_line_variant = |item: &ListItem| -> bool {
             let variant_str = item.inner_as_ref();
+            if self.config.style_edition() < StyleEdition::Edition2024 {
+                // Fall back to previous naive implementation (#5662) because of
+                // rustfmt's stability guarantees
+                return variant_str.contains('\n');
+            }
+
             let mut first_line_is_read = false;
             for line in variant_str.split('\n') {
                 if first_line_is_read {
@@ -663,7 +669,7 @@ impl<'a> FmtVisitor<'a> {
             }
 
             true
-        }
+        };
         let has_multiline_variant = items.iter().any(is_multi_line_variant);
         let has_single_line_variant = items.iter().any(|item| !is_multi_line_variant(item));
         if has_multiline_variant && has_single_line_variant {
diff --git a/tests/target/attribute-in-enum/horizontal-no-doc.rs b/tests/target/attribute-in-enum/horizontal-no-doc.rs
index f869c902cc4..56c378cea97 100644
--- a/tests/target/attribute-in-enum/horizontal-no-doc.rs
+++ b/tests/target/attribute-in-enum/horizontal-no-doc.rs
@@ -1,3 +1,4 @@
+// rustfmt-style_edition: 2024
 enum MyType {
     A { field1: bool, field2: bool },
     B { field1: bool, field2: bool },
diff --git a/tests/target/attribute-in-enum/horizontal-with-doc.rs b/tests/target/attribute-in-enum/horizontal-with-doc.rs
index cbf1dc78e65..0a0b374e76d 100644
--- a/tests/target/attribute-in-enum/horizontal-with-doc.rs
+++ b/tests/target/attribute-in-enum/horizontal-with-doc.rs
@@ -1,3 +1,4 @@
+// rustfmt-style_edition: 2024
 enum MyType {
     A { field1: bool, field2: bool },
     B { field1: bool, field2: bool },
diff --git a/tests/target/attribute-in-enum/vertical-macro-one-line.rs b/tests/target/attribute-in-enum/vertical-macro-one-line.rs
index a6669b3003e..e7cfe64a1db 100644
--- a/tests/target/attribute-in-enum/vertical-macro-one-line.rs
+++ b/tests/target/attribute-in-enum/vertical-macro-one-line.rs
@@ -1,3 +1,4 @@
+// rustfmt-style_edition: 2024
 enum A {
     B {
         a: usize,
diff --git a/tests/target/attribute-in-enum/vertical-no-doc.rs b/tests/target/attribute-in-enum/vertical-no-doc.rs
index 1148c03a008..2369bc368b7 100644
--- a/tests/target/attribute-in-enum/vertical-no-doc.rs
+++ b/tests/target/attribute-in-enum/vertical-no-doc.rs
@@ -1,3 +1,4 @@
+// rustfmt-style_edition: 2024
 enum A {
     B {
         a: usize,
diff --git a/tests/target/attribute-in-enum/vertical-with-doc.rs b/tests/target/attribute-in-enum/vertical-with-doc.rs
index b61a018ac12..7b1d3315c2b 100644
--- a/tests/target/attribute-in-enum/vertical-with-doc.rs
+++ b/tests/target/attribute-in-enum/vertical-with-doc.rs
@@ -1,3 +1,4 @@
+// rustfmt-style_edition: 2024
 enum A {
     B {
         a: usize,