diff --git a/crates/ide_assists/src/handlers/merge_match_arms.rs b/crates/ide_assists/src/handlers/merge_match_arms.rs
index 5c6bb986b9..0ebc5d267c 100644
--- a/crates/ide_assists/src/handlers/merge_match_arms.rs
+++ b/crates/ide_assists/src/handlers/merge_match_arms.rs
@@ -72,7 +72,7 @@ pub(crate) fn merge_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option
                     .join(" | ")
             };
 
-            let arm = format!("{} => {}", pats, current_expr.syntax().text());
+            let arm = format!("{} => {},", pats, current_expr.syntax().text());
 
             if let [first, .., last] = &*arms_to_merge {
                 let start = first.syntax().text_range().start();
@@ -118,7 +118,7 @@ enum X { A, B, C }
 fn main() {
     let x = X::A;
     let y = match x {
-        X::A | X::B => { 1i32 }
+        X::A | X::B => { 1i32 },
         X::C => { 2i32 }
     }
 }
@@ -183,7 +183,7 @@ fn main() {
     let x = X::A;
     let y = match x {
         X::A => { 1i32 },
-        _ => { 2i32 }
+        _ => { 2i32 },
     }
 }
 "#,
diff --git a/crates/ide_diagnostics/src/handlers/inactive_code.rs b/crates/ide_diagnostics/src/handlers/inactive_code.rs
index dfd0e33519..b6a7aee59e 100644
--- a/crates/ide_diagnostics/src/handlers/inactive_code.rs
+++ b/crates/ide_diagnostics/src/handlers/inactive_code.rs
@@ -64,7 +64,7 @@ fn f() {
     match () {
         () => (),
         #[cfg(a)] () => (),
-      //^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
+      //^^^^^^^^^^^^^^^^^^^ weak: code is inactive due to #[cfg] directives: a is disabled
     }
 
     #[cfg(a)] 0          // Trailing expression of block
diff --git a/crates/syntax/src/ast/edit_in_place.rs b/crates/syntax/src/ast/edit_in_place.rs
index 30af469bc7..e9280ab45c 100644
--- a/crates/syntax/src/ast/edit_in_place.rs
+++ b/crates/syntax/src/ast/edit_in_place.rs
@@ -359,14 +359,10 @@ impl ast::MatchArmList {
         let mut elements = Vec::new();
         let position = match self.arms().last() {
             Some(last_arm) => {
-                let comma = last_arm
-                    .syntax()
-                    .siblings_with_tokens(Direction::Next)
-                    .find(|it| it.kind() == T![,]);
-                if needs_comma(&last_arm) && comma.is_none() {
-                    elements.push(make::token(SyntaxKind::COMMA).into());
+                if needs_comma(&last_arm) {
+                    ted::append_child(last_arm.syntax(), make::token(SyntaxKind::COMMA));
                 }
-                Position::after(comma.unwrap_or_else(|| last_arm.syntax().clone().into()))
+                Position::after(last_arm.syntax().clone())
             }
             None => match self.l_curly_token() {
                 Some(it) => Position::after(it),
@@ -377,12 +373,12 @@ impl ast::MatchArmList {
         elements.push(make::tokens::whitespace(&format!("\n{}", indent)).into());
         elements.push(arm.syntax().clone().into());
         if needs_comma(&arm) {
-            elements.push(make::token(SyntaxKind::COMMA).into());
+            ted::append_child(arm.syntax(), make::token(SyntaxKind::COMMA));
         }
         ted::insert_all(position, elements);
 
         fn needs_comma(arm: &ast::MatchArm) -> bool {
-            arm.expr().map_or(false, |e| !e.is_block_like())
+            arm.expr().map_or(false, |e| !e.is_block_like()) && arm.comma_token().is_none()
         }
     }
 }