diff --git a/changes/operand-line-comment.fix.md b/changes/operand-line-comment.fix.md
new file mode 100644
index 0000000000..28f4f60ed3
--- /dev/null
+++ b/changes/operand-line-comment.fix.md
@@ -0,0 +1 @@
+- Keep a line comment in the operand of `switch`, `if`, `try` or a loop in the operand instead of moving it into the block when formatting.
diff --git a/compiler/syntax/src/res_doc.ml b/compiler/syntax/src/res_doc.ml
index e2222c2288..5ba1a50e8c 100644
--- a/compiler/syntax/src/res_doc.ml
+++ b/compiler/syntax/src/res_doc.ml
@@ -122,6 +122,25 @@ let rec will_break doc =
   | IfBreaks {yes; no} -> will_break yes || will_break no
   | _ -> false
 
+(* See documentation in interface file *)
+let has_pending_line_suffix doc =
+  (* [pending]: a line suffix is queued; [broken]: the innermost enclosing
+     group is printed in break mode, so its line breaks flush the queue. *)
+  let rec walk ~broken pending doc =
+    match doc with
+    | LineSuffix _ -> true
+    | LineBreak _ -> pending && not broken
+    | Nil | Text _ | BreakParent -> pending
+    | Indent doc -> walk ~broken pending doc
+    | Concat docs -> List.fold_left (walk ~broken) pending docs
+    | Group {should_break; doc} ->
+      walk ~broken:(should_break || will_break doc) pending doc
+    | IfBreaks {yes; no; broken = if_broken} ->
+      walk ~broken pending (if broken || if_broken then yes else no)
+    | CustomLayout docs -> List.exists (walk ~broken:false pending) docs
+  in
+  walk ~broken:false false doc
+
 let join ~sep docs =
   let rec loop acc sep docs =
     match docs with
diff --git a/compiler/syntax/src/res_doc.mli b/compiler/syntax/src/res_doc.mli
index d3423658c0..13caa1a0c2 100644
--- a/compiler/syntax/src/res_doc.mli
+++ b/compiler/syntax/src/res_doc.mli
@@ -50,6 +50,13 @@ val will_break : t -> bool
     [will_break] to detect a forced break in a custom layout and explicitly add
     [break_parent] to propagate it to the parent document. *)
 
+val has_pending_line_suffix : t -> bool
+(** [has_pending_line_suffix doc] checks whether a line suffix (a trailing line
+    comment) in [doc] is still queued at its end, because no line break of a
+    group that breaks follows it. Groups that only break for lack of width
+    count as flat. Text after [doc] on the same line would precede the
+    comment. *)
+
 val to_string : width:int -> t -> string
 val debug : t -> unit
 
diff --git a/compiler/syntax/src/res_printer.ml b/compiler/syntax/src/res_printer.ml
index ed4327dc01..2df53ca625 100644
--- a/compiler/syntax/src/res_printer.ml
+++ b/compiler/syntax/src/res_printer.ml
@@ -3165,6 +3165,38 @@ and print_expression_args ~state (args : Parsetree.expression list) cmt_tbl =
         Doc.rparen;
       ]
 
+(* The operand of [switch], [try], [if], [while] or a loop, which is followed
+   by more code on the same line. A line comment still pending at its end
+   would move after that code, into the block, so the operand goes into
+   parentheses with the comment before the [)]. *)
+and print_operand_before_brace doc =
+  if Doc.has_pending_line_suffix doc then add_operand_parens doc else doc
+
+(* An operand followed by a block, see [print_operand_before_brace], with the
+   parentheses or braces it needs *)
+and print_block_operand ~state expr cmt_tbl =
+  let doc = print_expression_with_comments ~state expr cmt_tbl in
+  print_operand_before_brace
+    (match Parens.expr expr with
+    | Parens.Parenthesized -> add_operand_parens doc
+    | Braced braces -> print_braces doc expr braces
+    | Nothing -> doc)
+
+(* Parentheses around such an operand, or around one that needs them, such as
+   a coercion. They break when a line comment is still pending at the end of
+   the operand, so that the comment stays before the [)]. *)
+and add_operand_parens doc =
+  if Doc.has_pending_line_suffix doc then
+    Doc.breakable_group ~force_break:true
+      (Doc.concat
+         [
+           Doc.lparen;
+           Doc.indent (Doc.concat [Doc.soft_line; doc]);
+           Doc.soft_line;
+           Doc.rparen;
+         ])
+  else add_parens doc
+
 and print_if_chain ~state pexp_attributes ifs else_expr cmt_tbl =
   let if_docs =
     Doc.join ~sep:Doc.space
@@ -3180,14 +3212,14 @@ and print_if_chain ~state pexp_attributes ifs else_expr cmt_tbl =
                    print_expression_with_comments ~state if_expr cmt_tbl
                  in
                  match Parens.expr if_expr with
-                 | Parens.Parenthesized -> add_parens doc
+                 | Parens.Parenthesized -> add_operand_parens doc
                  | Braced braces -> print_braces doc if_expr braces
                  | Nothing -> Doc.if_breaks (add_parens doc) doc
              in
              Doc.concat
                [
                  if_txt;
-                 Doc.group condition;
+                 print_operand_before_brace (Doc.group condition);
                  Doc.space;
                  (let then_expr =
                     match Parsetree_viewer.process_braces then_expr with
@@ -3659,7 +3691,7 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
       let condition =
         let doc = print_expression_with_comments ~state expr1 cmt_tbl in
         match Parens.expr expr1 with
-        | Parens.Parenthesized -> add_parens doc
+        | Parens.Parenthesized -> add_operand_parens doc
         | Braced braces -> print_braces doc expr1 braces
         | Nothing -> doc
       in
@@ -3667,8 +3699,11 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
         (Doc.concat
            [
              Doc.text "while ";
-             (if Parsetree_viewer.is_block_expr expr1 then condition
-              else Doc.group (Doc.if_breaks (add_parens condition) condition));
+             print_operand_before_brace
+               (match Parens.expr expr1 with
+               | Parens.Parenthesized -> condition
+               | _ when Parsetree_viewer.is_block_expr expr1 -> condition
+               | _ -> Doc.group (Doc.if_breaks (add_parens condition) condition));
              Doc.space;
              print_expression_block ~state ~braces:true expr2 cmt_tbl;
            ])
@@ -3679,19 +3714,9 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
              Doc.text "for ";
              print_pattern ~state pattern cmt_tbl;
              Doc.text " in ";
-             (let doc =
-                print_expression_with_comments ~state from_expr cmt_tbl
-              in
-              match Parens.expr from_expr with
-              | Parens.Parenthesized -> add_parens doc
-              | Braced braces -> print_braces doc from_expr braces
-              | Nothing -> doc);
+             print_block_operand ~state from_expr cmt_tbl;
              print_direction_flag direction_flag;
-             (let doc = print_expression_with_comments ~state to_expr cmt_tbl in
-              match Parens.expr to_expr with
-              | Parens.Parenthesized -> add_parens doc
-              | Braced braces -> print_braces doc to_expr braces
-              | Nothing -> doc);
+             print_block_operand ~state to_expr cmt_tbl;
              Doc.space;
              print_expression_block ~state ~braces:true body cmt_tbl;
            ])
@@ -3702,13 +3727,7 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
              Doc.text "for ";
              print_pattern ~state pattern cmt_tbl;
              Doc.text " of ";
-             (let doc =
-                print_expression_with_comments ~state array_expr cmt_tbl
-              in
-              match Parens.expr array_expr with
-              | Parens.Parenthesized -> add_parens doc
-              | Braced braces -> print_braces doc array_expr braces
-              | Nothing -> doc);
+             print_block_operand ~state array_expr cmt_tbl;
              Doc.space;
              print_expression_block ~state ~braces:true body cmt_tbl;
            ])
@@ -3719,13 +3738,7 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
              Doc.text "for await ";
              print_pattern ~state pattern cmt_tbl;
              Doc.text " of ";
-             (let doc =
-                print_expression_with_comments ~state iterable_expr cmt_tbl
-              in
-              match Parens.expr iterable_expr with
-              | Parens.Parenthesized -> add_parens doc
-              | Braced braces -> print_braces doc iterable_expr braces
-              | Nothing -> doc);
+             print_block_operand ~state iterable_expr cmt_tbl;
              Doc.space;
              print_expression_block ~state ~braces:true body cmt_tbl;
            ])
@@ -3805,13 +3818,7 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
     | Pexp_sequence _ -> print_expression_block ~state ~braces:true e cmt_tbl
     | Pexp_let _ -> print_expression_block ~state ~braces:true e cmt_tbl
     | Pexp_try (expr, cases, finally) ->
-      let expr_doc =
-        let doc = print_expression_with_comments ~state expr cmt_tbl in
-        match Parens.expr expr with
-        | Parens.Parenthesized -> add_parens doc
-        | Braced braces -> print_braces doc expr braces
-        | Nothing -> doc
-      in
+      let expr_doc = print_block_operand ~state expr cmt_tbl in
       let catch_doc =
         match cases with
         | [] -> Doc.nil
@@ -3830,13 +3837,7 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
       in
       Doc.concat [Doc.text "try "; expr_doc; catch_doc; finally_doc]
     | Pexp_match (expr, cases) ->
-      let expr_doc =
-        let doc = print_expression_with_comments ~state expr cmt_tbl in
-        match Parens.expr expr with
-        | Parens.Parenthesized -> add_parens doc
-        | Braced braces -> print_braces doc expr braces
-        | Nothing -> doc
-      in
+      let expr_doc = print_block_operand ~state expr cmt_tbl in
       Doc.concat
         [
           Doc.text "switch ";
diff --git a/tests/syntax_tests/data/printer/comments/expected/operandLineComment.res.txt b/tests/syntax_tests/data/printer/comments/expected/operandLineComment.res.txt
new file mode 100644
index 0000000000..f00f09f6b5
--- /dev/null
+++ b/tests/syntax_tests/data/printer/comments/expected/operandLineComment.res.txt
@@ -0,0 +1,227 @@
+// A line comment in the operand of a block construct stays in the operand
+
+switch (
+  obj.x // c
+) {
+| _ => ()
+}
+
+switch (
+  obj.x.y // c
+) {
+| _ => ()
+}
+
+switch (
+  obj.x.y // c // d
+) {
+| _ => ()
+}
+
+switch (
+  arr[0] // c
+) {
+| _ => ()
+}
+
+switch (
+  obj["member"] // c
+) {
+| _ => ()
+}
+
+switch (
+  obj["member"] // c
+) {
+| _ => ()
+}
+
+switch (
+  obj->f // c
+) {
+| _ => ()
+}
+
+switch (
+  a + b // c
+) {
+| _ => ()
+}
+
+switch f(
+  // c
+  x,
+) {
+| _ => ()
+}
+
+switch x {
+// c
+| _ => ()
+}
+
+if (
+  obj.x // c
+) {
+  ()
+} else if (
+  obj.y // d
+) {
+  ()
+}
+
+while (
+  obj.x // c
+) {
+  ()
+}
+
+for x of (
+  obj.x // c
+) {
+  ()
+}
+
+let f = async () => {
+  for await x of (
+    obj.x // c
+  ) {
+    ()
+  }
+}
+
+for i in (
+  0 // c
+) to n {
+  ()
+}
+
+for i in 0 to (
+  n // c
+) {
+  ()
+}
+
+try (
+  obj.x // c
+) catch {
+| _ => ()
+}
+
+// An operand printed in its own parentheses keeps the comment inside them
+switch (
+  f(a, b) :> int // c
+) {
+| _ => ()
+}
+
+switch (
+  f(a, b): int // c
+) {
+| _ => ()
+}
+
+if (
+  f(a, b) :> bool // c
+) {
+  ()
+}
+
+while (
+  f(a, b) :> bool // c
+) {
+  ()
+}
+
+for x of (
+  f(a, b) :> array<int> // c
+) {
+  ()
+}
+
+try (
+  f(a, b) :> int // c
+) catch {
+| _ => ()
+}
+
+// A comment after an item of the operand
+switch (
+  [a, b] // c // d
+) {
+| _ => ()
+}
+
+switch (
+  list{a, ...b, ...c} // c
+) {
+| _ => ()
+}
+
+switch (
+  (a, b) // c
+) {
+| _ => ()
+}
+
+switch {
+  x: a, // c
+  y: b,
+} {
+| _ => ()
+}
+
+switch (
+  a->f(x, y) // c
+) {
+| _ => ()
+}
+
+switch (
+  a->f(x, y) // c // d
+) {
+| _ => ()
+}
+
+if (
+  f(a, b) // c
+) {
+  ()
+}
+
+while (
+  f(a, b) + 1 > 0 // c
+) {
+  ()
+}
+
+for x of (
+  [a, b] // c
+) {
+  ()
+}
+
+try (
+  [...a, b] // c
+) catch {
+| _ => ()
+}
+
+// A binary expression or pipe in an item of the operand
+switch (
+  [a + b, d] // c
+) {
+| _ => ()
+}
+
+if (
+  f(a && b) // c
+) {
+  ()
+}
+
+for x of (
+  [a->f(y)] // c
+) {
+  ()
+}
diff --git a/tests/syntax_tests/data/printer/comments/operandLineComment.res b/tests/syntax_tests/data/printer/comments/operandLineComment.res
new file mode 100644
index 0000000000..b9d09a6bd3
--- /dev/null
+++ b/tests/syntax_tests/data/printer/comments/operandLineComment.res
@@ -0,0 +1,223 @@
+// A line comment in the operand of a block construct stays in the operand
+
+switch obj // c
+.x {
+| _ => ()
+}
+
+switch obj // c
+.x.y {
+| _ => ()
+}
+
+switch obj // c
+.x // d
+.y {
+| _ => ()
+}
+
+switch arr[// c
+0] {
+| _ => ()
+}
+
+switch obj[// c
+"member"] {
+| _ => ()
+}
+
+switch obj["member"] // c
+{
+| _ => ()
+}
+
+switch obj // c
+->f {
+| _ => ()
+}
+
+switch a // c
++ b {
+| _ => ()
+}
+
+switch f(// c
+x) {
+| _ => ()
+}
+
+switch x { // c
+| _ => ()
+}
+
+if obj // c
+.x {
+  ()
+} else if obj // d
+.y {
+  ()
+}
+
+while obj // c
+.x {
+  ()
+}
+
+for x of obj // c
+.x {
+  ()
+}
+
+let f = async () => {
+  for await x of obj // c
+  .x {
+    ()
+  }
+}
+
+for i in 0 // c
+to n {
+  ()
+}
+
+for i in 0 to n // c
+{
+  ()
+}
+
+try obj // c
+.x catch {
+| _ => ()
+}
+
+// An operand printed in its own parentheses keeps the comment inside them
+switch (f(
+  a, // c
+  b,
+) :> int) {
+| _ => ()
+}
+
+switch (f(
+  a, // c
+  b,
+): int) {
+| _ => ()
+}
+
+if (f(
+  a, // c
+  b,
+) :> bool) {
+  ()
+}
+
+while (f(
+  a, // c
+  b,
+) :> bool) {
+  ()
+}
+
+for x of (f(
+  a, // c
+  b,
+) :> array<int>) {
+  ()
+}
+
+try (f(
+  a, // c
+  b,
+) :> int) catch {
+| _ => ()
+}
+
+// A comment after an item of the operand
+switch [
+  a, // c
+  b, // d
+] {
+| _ => ()
+}
+
+switch list{
+  a, // c
+  ...b,
+  ...c,
+} {
+| _ => ()
+}
+
+switch (
+  a, // c
+  b,
+) {
+| _ => ()
+}
+
+switch {
+  x: a, // c
+  y: b,
+} {
+| _ => ()
+}
+
+switch a->f(
+  x, // c
+  y,
+) {
+| _ => ()
+}
+
+switch a // c
+->f(
+  x, // d
+  y,
+) {
+| _ => ()
+}
+
+if f(
+  a, // c
+  b,
+) {
+  ()
+}
+
+while f(
+  a, // c
+  b,
+) + 1 > 0 {
+  ()
+}
+
+for x of [
+  a, // c
+  b,
+] {
+  ()
+}
+
+try [
+  ...a, // c
+  b,
+] catch {
+| _ => ()
+}
+
+// A binary expression or pipe in an item of the operand
+switch [a // c
++ b, d] {
+| _ => ()
+}
+
+if f(a // c
+&& b) {
+  ()
+}
+
+for x of [a // c
+->f(y)] {
+  ()
+}