diff --git a/clippy_lints/src/lines_filter_map_ok.rs b/clippy_lints/src/lines_filter_map_ok.rs
index 0a5f5a80cb72..00ca553445fc 100644
--- a/clippy_lints/src/lines_filter_map_ok.rs
+++ b/clippy_lints/src/lines_filter_map_ok.rs
@@ -53,18 +53,45 @@ declare_clippy_lint! {
     #[clippy::version = "1.70.0"]
     pub LINES_FILTER_MAP_OK,
     suspicious,
-    "filtering `std::io::Lines` with `filter_map()` or `flat_map()` might cause an infinite loop"
+    "filtering `std::io::Lines` with `filter_map()`, `flat_map()`, or `flatten()` might cause an infinite loop"
 }
 declare_lint_pass!(LinesFilterMapOk => [LINES_FILTER_MAP_OK]);
 
 impl LateLintPass<'_> for LinesFilterMapOk {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
-        if let ExprKind::MethodCall(fm_method, fm_receiver, [fm_arg], fm_span) = expr.kind
+        if let ExprKind::MethodCall(fm_method, fm_receiver, fm_args, fm_span) = expr.kind
             && is_trait_method(cx, expr, sym::Iterator)
-            && (fm_method.ident.as_str() == "filter_map" || fm_method.ident.as_str() == "flat_map")
+            && let fm_method_str = fm_method.ident.as_str()
+            && matches!(fm_method_str, "filter_map" | "flat_map" | "flatten")
             && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty_adjusted(fm_receiver), sym::IoLines)
+            && should_lint(cx, fm_args, fm_method_str)
         {
-            let lint = match &fm_arg.kind {
+            span_lint_and_then(
+                cx,
+                LINES_FILTER_MAP_OK,
+                fm_span,
+                &format!("`{fm_method_str}()` will run forever if the iterator repeatedly produces an `Err`",),
+                |diag| {
+                    diag.span_note(
+                        fm_receiver.span,
+                        "this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error");
+                    diag.span_suggestion(
+                        fm_span,
+                        "replace with",
+                        "map_while(Result::ok)",
+                        Applicability::MaybeIncorrect,
+                    );
+                },
+            );
+        }
+    }
+}
+
+fn should_lint(cx: &LateContext<'_>, args: &[Expr<'_>], method_str: &str) -> bool {
+    match args {
+        [] => method_str == "flatten",
+        [fm_arg] => {
+            match &fm_arg.kind {
                 // Detect `Result::ok`
                 ExprKind::Path(qpath) => cx
                     .qpath_res(qpath, fm_arg.hir_id)
@@ -86,29 +113,8 @@ impl LateLintPass<'_> for LinesFilterMapOk {
                     }
                 },
                 _ => false,
-            };
-            if lint {
-                span_lint_and_then(
-                    cx,
-                    LINES_FILTER_MAP_OK,
-                    fm_span,
-                    &format!(
-                        "`{}()` will run forever if the iterator repeatedly produces an `Err`",
-                        fm_method.ident
-                    ),
-                    |diag| {
-                        diag.span_note(
-                            fm_receiver.span,
-                            "this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error");
-                        diag.span_suggestion(
-                            fm_span,
-                            "replace with",
-                            "map_while(Result::ok)",
-                            Applicability::MaybeIncorrect,
-                        );
-                    },
-                );
             }
-        }
+        },
+        _ => false,
     }
 }
diff --git a/tests/ui/lines_filter_map_ok.fixed b/tests/ui/lines_filter_map_ok.fixed
index 74ef6f72957f..621115cc1325 100644
--- a/tests/ui/lines_filter_map_ok.fixed
+++ b/tests/ui/lines_filter_map_ok.fixed
@@ -10,11 +10,17 @@ fn main() -> io::Result<()> {
     // Lint
     let f = std::fs::File::open("/")?;
     BufReader::new(f).lines().map_while(Result::ok).for_each(|_| ());
+    // Lint
+    let f = std::fs::File::open("/")?;
+    BufReader::new(f).lines().map_while(Result::ok).for_each(|_| ());
+
     let s = "foo\nbar\nbaz\n";
     // Lint
     io::stdin().lines().map_while(Result::ok).for_each(|_| ());
     // Lint
     io::stdin().lines().map_while(Result::ok).for_each(|_| ());
+    // Lint
+    io::stdin().lines().map_while(Result::ok).for_each(|_| ());
     // Do not lint (not a `Lines` iterator)
     io::stdin()
         .lines()
diff --git a/tests/ui/lines_filter_map_ok.rs b/tests/ui/lines_filter_map_ok.rs
index 345f4dc5f304..a86efbd66862 100644
--- a/tests/ui/lines_filter_map_ok.rs
+++ b/tests/ui/lines_filter_map_ok.rs
@@ -10,11 +10,17 @@ fn main() -> io::Result<()> {
     // Lint
     let f = std::fs::File::open("/")?;
     BufReader::new(f).lines().flat_map(Result::ok).for_each(|_| ());
+    // Lint
+    let f = std::fs::File::open("/")?;
+    BufReader::new(f).lines().flatten().for_each(|_| ());
+
     let s = "foo\nbar\nbaz\n";
     // Lint
     io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
     // Lint
     io::stdin().lines().filter_map(|x| x.ok()).for_each(|_| ());
+    // Lint
+    io::stdin().lines().flatten().for_each(|_| ());
     // Do not lint (not a `Lines` iterator)
     io::stdin()
         .lines()
diff --git a/tests/ui/lines_filter_map_ok.stderr b/tests/ui/lines_filter_map_ok.stderr
index fa2ba0a9a462..9833ab16473c 100644
--- a/tests/ui/lines_filter_map_ok.stderr
+++ b/tests/ui/lines_filter_map_ok.stderr
@@ -24,29 +24,53 @@ note: this expression returning a `std::io::Lines` may produce an infinite numbe
 LL |     BufReader::new(f).lines().flat_map(Result::ok).for_each(|_| ());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
-  --> $DIR/lines_filter_map_ok.rs:15:25
+error: `flatten()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:15:31
    |
-LL |     io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
-   |                         ^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+LL |     BufReader::new(f).lines().flatten().for_each(|_| ());
+   |                               ^^^^^^^^^ help: replace with: `map_while(Result::ok)`
    |
 note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
   --> $DIR/lines_filter_map_ok.rs:15:5
    |
+LL |     BufReader::new(f).lines().flatten().for_each(|_| ());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:19:25
+   |
+LL |     io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
+   |                         ^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+   |
+note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
+  --> $DIR/lines_filter_map_ok.rs:19:5
+   |
 LL |     io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
    |     ^^^^^^^^^^^^^^^^^^^
 
 error: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
-  --> $DIR/lines_filter_map_ok.rs:17:25
+  --> $DIR/lines_filter_map_ok.rs:21:25
    |
 LL |     io::stdin().lines().filter_map(|x| x.ok()).for_each(|_| ());
    |                         ^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
    |
 note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
-  --> $DIR/lines_filter_map_ok.rs:17:5
+  --> $DIR/lines_filter_map_ok.rs:21:5
    |
 LL |     io::stdin().lines().filter_map(|x| x.ok()).for_each(|_| ());
    |     ^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: `flatten()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:23:25
+   |
+LL |     io::stdin().lines().flatten().for_each(|_| ());
+   |                         ^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+   |
+note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
+  --> $DIR/lines_filter_map_ok.rs:23:5
+   |
+LL |     io::stdin().lines().flatten().for_each(|_| ());
+   |     ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors