diff --git a/src/formatters/assignment.rs b/src/formatters/assignment.rs
index 3983e7c4..c284c9d2 100644
--- a/src/formatters/assignment.rs
+++ b/src/formatters/assignment.rs
@@ -18,7 +18,7 @@ use crate::{
     context::{create_indent_trivia, create_newline_trivia, Context},
     fmt_symbol,
     formatters::{
-        expression::{format_expression, format_var, hang_expression},
+        expression::{format_expression, format_var, hang_expression, is_brackets_string},
         general::{
             format_punctuated, format_punctuated_multiline, format_token_reference,
             try_format_punctuated,
@@ -201,6 +201,29 @@ pub fn hang_at_equals_due_to_comments(
     (equal_token, expression)
 }
 
+/// Whether the expression is a `..` chain whose leftmost operand is a multiline long string (`[[ ]]` / `[=[ ]=]`)
+fn is_multiline_long_string_concat(expression: &Expression) -> bool {
+    fn leftmost(expression: &Expression) -> &Expression {
+        match expression {
+            Expression::BinaryOperator { lhs, .. } => leftmost(lhs),
+            _ => expression,
+        }
+    }
+
+    matches!(
+        expression,
+        Expression::BinaryOperator {
+            binop: full_moon::ast::BinOp::TwoDots(_),
+            ..
+        }
+    ) && match leftmost(expression) {
+        Expression::String(token) => {
+            is_brackets_string(leftmost(expression)) && token.token().to_string().contains('\n')
+        }
+        _ => false,
+    }
+}
+
 /// Attempts different formatting tactics on an expression list being assigned (`= foo, bar`), to find the best
 /// formatting output.
 fn attempt_assignment_tactics(
@@ -297,8 +320,14 @@ fn attempt_assignment_tactics(
             let hanging_expr_list = hang_punctuated_list(ctx, expressions, shape);
             let hanging_shape = shape.take_first_line(&strip_trivia(&hanging_expr_list));
 
+            // A `..` chain led by a multiline long string (e.g. `[[ ]]`) has a short first line, so the
+            // comparison above never hangs it, even when a later line is over budget. Only hang if that fixes it
             if expression.has_inline_comments()
                 || hanging_shape.used_width() < formatting_shape.used_width()
+                // Check the formatted expression (e.g. with parentheses removed), as that is what is output
+                || (is_multiline_long_string_concat(expr_list.iter().next().unwrap())
+                    && shape.test_over_budget(&strip_trailing_trivia(&expr_list))
+                    && !shape.test_over_budget(&strip_trivia(&hanging_expr_list)))
             {
                 (hanging_expr_list, equal_token)
             } else {
diff --git a/tests/inputs/concat-multiline-string-chain.lua b/tests/inputs/concat-multiline-string-chain.lua
new file mode 100644
index 00000000..c2a2f42a
--- /dev/null
+++ b/tests/inputs/concat-multiline-string-chain.lua
@@ -0,0 +1,30 @@
+local x = [[
+box[0,0;1,1;]
+dropdown[4,0.75;6.4;contributor_grouping;]] .. S("Group by name") .. "," .. S("Group by contribution") .. ";" .. mail.selected_idxs.contributor_grouping[name] .. [[;true]
+]]
+local y = "dropdown[4,0.75;6.4;contributor_grouping;" .. S("Group by name") .. "," .. S("Group by contribution") .. ";" .. mail.selected_idxs.contributor_grouping[name] .. ";true]"
+local z = [[
+short]] .. foo .. [[bar]]
+x = [[
+box[0,0;1,1;]
+dropdown[4,0.75;6.4;contributor_grouping;]] .. S("Group by name") .. "," .. S("Group by contribution") .. ";" .. mail.selected_idxs.contributor_grouping[name] .. [[;true]
+]]
+-- regression: function-led multiline RHS must be unchanged
+local f = (function()
+  return 1
+end)() .. "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" .. b
+-- regression: call-led multiline RHS (reduced from jest-lua TestScheduler) must be unchanged
+local function g()
+	local message = ("%sYour test suite is leaking memory. Please ensure all references are cleaned.\n"):format(
+		tostring(chalk.red:bold("EXPERIMENTAL FEATURE!\n"))
+	) .. "\n" .. "There is a number of things that can leak memory:\n" .. "  - Async operations that have not finished (e.g. fs.readFile).\n" .. "  - Keeping references to the global scope."
+end
+-- regression: over-long line inside the long string itself; hanging cannot help, so must be unchanged
+local s = [[
+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+]] .. a .. b
+-- parenthesised long string lead: parentheses are removed, so the chain must hang in a single pass
+local p = ([[
+foo
+]]) .. "dropdown[4,0.75;6.4;contributor_grouping;" .. S("Group by name") .. "," .. S("Group by contribution") .. ";" .. mail.selected_idxs.contributor_grouping[name] .. [[;true]
+]]
diff --git a/tests/snapshots/tests__standard@concat-multiline-string-chain.lua.snap b/tests/snapshots/tests__standard@concat-multiline-string-chain.lua.snap
new file mode 100644
index 00000000..bcf0c13e
--- /dev/null
+++ b/tests/snapshots/tests__standard@concat-multiline-string-chain.lua.snap
@@ -0,0 +1,61 @@
+---
+source: tests/tests.rs
+expression: "format(&contents, LuaVersion::Lua51)"
+input_file: tests/inputs/concat-multiline-string-chain.lua
+---
+local x = [[
+box[0,0;1,1;]
+dropdown[4,0.75;6.4;contributor_grouping;]]
+	.. S("Group by name")
+	.. ","
+	.. S("Group by contribution")
+	.. ";"
+	.. mail.selected_idxs.contributor_grouping[name]
+	.. [[;true]
+]]
+local y = "dropdown[4,0.75;6.4;contributor_grouping;"
+	.. S("Group by name")
+	.. ","
+	.. S("Group by contribution")
+	.. ";"
+	.. mail.selected_idxs.contributor_grouping[name]
+	.. ";true]"
+local z = [[
+short]] .. foo .. [[bar]]
+x = [[
+box[0,0;1,1;]
+dropdown[4,0.75;6.4;contributor_grouping;]]
+	.. S("Group by name")
+	.. ","
+	.. S("Group by contribution")
+	.. ";"
+	.. mail.selected_idxs.contributor_grouping[name]
+	.. [[;true]
+]]
+-- regression: function-led multiline RHS must be unchanged
+local f = (function()
+	return 1
+end)() .. "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" .. b
+-- regression: call-led multiline RHS (reduced from jest-lua TestScheduler) must be unchanged
+local function g()
+	local message = ("%sYour test suite is leaking memory. Please ensure all references are cleaned.\n"):format(
+		tostring(chalk.red:bold("EXPERIMENTAL FEATURE!\n"))
+	) .. "\n" .. "There is a number of things that can leak memory:\n" .. "  - Async operations that have not finished (e.g. fs.readFile).\n" .. "  - Keeping references to the global scope."
+end
+-- regression: over-long line inside the long string itself; hanging cannot help, so must be unchanged
+local s = [[
+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+]] .. a .. b
+-- parenthesised long string lead: parentheses are removed, so the chain must hang in a single pass
+local p = [[
+foo
+]]
+	.. "dropdown[4,0.75;6.4;contributor_grouping;"
+	.. S("Group by name")
+	.. ","
+	.. S("Group by contribution")
+	.. ";"
+	.. mail.selected_idxs.contributor_grouping[name]
+	.. [[;true]
+]]
+
diff --git a/tests/test_concat_idempotence.rs b/tests/test_concat_idempotence.rs
new file mode 100644
index 00000000..6bffaa77
--- /dev/null
+++ b/tests/test_concat_idempotence.rs
@@ -0,0 +1,10 @@
+use stylua_lib::{format_code, Config, OutputVerification};
+
+#[test]
+fn test_concat_multiline_string_chain_idempotent() {
+    let input = include_str!("inputs/concat-multiline-string-chain.lua");
+    let format =
+        |code: &str| format_code(code, Config::default(), None, OutputVerification::None).unwrap();
+    let first = format(input);
+    assert_eq!(format(&first), first);
+}