diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 755a7dc07..9ef1fe153 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -3991,6 +3991,8 @@ pub fn insert_newline(cx: &mut Context) {
         let mut global_offs = 0;
 
         let mut transaction = Transaction::change_by_selection(contents, &selection, |range| {
+            // Tracks the number of trailing whitespace characters deleted by this selection.
+            let mut chars_deleted = 0;
             let pos = range.cursor(text);
 
             let prev = if pos == 0 {
@@ -4069,13 +4071,14 @@ pub fn insert_newline(cx: &mut Context) {
                     new_text.chars().count()
                 };
 
+                // Note that `first_trailing_whitespace_char` is at least `pos` so this unsigned
+                // subtraction cannot underflow.
+                chars_deleted = pos - first_trailing_whitespace_char;
+
                 (
                     first_trailing_whitespace_char,
                     pos,
-                    // Note that `first_trailing_whitespace_char` is at least `pos` so the
-                    // unsigned subtraction (`pos - first_trailing_whitespace_char`) cannot
-                    // underflow.
-                    local_offs as isize - (pos - first_trailing_whitespace_char) as isize,
+                    local_offs as isize - chars_deleted as isize,
                 )
             } else {
                 // If the current line is all whitespace, insert a line ending at the beginning of
@@ -4089,14 +4092,14 @@ pub fn insert_newline(cx: &mut Context) {
             let new_range = if range.cursor(text) > range.anchor {
                 // when appending, extend the range by local_offs
                 Range::new(
-                    range.anchor + global_offs,
-                    (range.head as isize + local_offs) as usize + global_offs,
+                    (range.anchor as isize + global_offs) as usize,
+                    (range.head as isize + local_offs + global_offs) as usize,
                 )
             } else {
                 // when inserting, slide the range by local_offs
                 Range::new(
-                    (range.anchor as isize + local_offs) as usize + global_offs,
-                    (range.head as isize + local_offs) as usize + global_offs,
+                    (range.anchor as isize + local_offs + global_offs) as usize,
+                    (range.head as isize + local_offs + global_offs) as usize,
                 )
             };
 
@@ -4104,7 +4107,7 @@ pub fn insert_newline(cx: &mut Context) {
             // range.replace(|range| range.is_empty(), head); -> fn extend if cond true, new head pos
             // can be used with cx.mode to do replace or extend on most changes
             ranges.push(new_range);
-            global_offs += new_text.chars().count();
+            global_offs += new_text.chars().count() as isize - chars_deleted as isize;
 
             (from, to, Some(new_text.into()))
         });
diff --git a/helix-term/tests/test/commands/insert.rs b/helix-term/tests/test/commands/insert.rs
index f23876dfb..9352f737f 100644
--- a/helix-term/tests/test/commands/insert.rs
+++ b/helix-term/tests/test/commands/insert.rs
@@ -1,5 +1,106 @@
 use super::*;
 
+#[tokio::test(flavor = "multi_thread")]
+async fn insert_newline_many_selections() -> anyhow::Result<()> {
+    test((
+        indoc! {"\
+            #(|o)#ne
+            #(|t)#wo
+            #[|t]#hree
+            "},
+        "i<ret>",
+        indoc! {"\
+            \n#(|o)#ne
+
+            #(|t)#wo
+
+            #[|t]#hree
+            "},
+    ))
+    .await?;
+
+    // In this case the global offset that adjusts selections for inserted and deleted text
+    // should become negative because more text is deleted than is inserted.
+    test((
+        indoc! {"\
+            #[|🏴‍☠️]#          #(|🏴‍☠️)#          #(|🏴‍☠️)#
+            #(|🏴‍☠️)#          #(|🏴‍☠️)#          #(|🏴‍☠️)#
+            "},
+        "i<ret>",
+        indoc! {"\
+            \n#[|🏴‍☠️]#
+            #(|🏴‍☠️)#
+            #(|🏴‍☠️)#
+
+            #(|🏴‍☠️)#
+            #(|🏴‍☠️)#
+            #(|🏴‍☠️)#
+            "},
+    ))
+    .await?;
+
+    // <https://github.com/helix-editor/helix/issues/12495>
+    test((
+        indoc! {"\
+            id #(|1)#,Item #(|1)#,cost #(|1)#,location #(|1)#
+            id #(|2)#,Item #(|2)#,cost #(|2)#,location #(|2)#
+            id #(|1)##(|0)#,Item #(|1)##(|0)#,cost #(|1)##(|0)#,location #(|1)##[|0]#"},
+        "i<ret>",
+        indoc! {"\
+            id
+            #(|1)#,Item
+            #(|1)#,cost
+            #(|1)#,location
+            #(|1)#
+            id
+            #(|2)#,Item
+            #(|2)#,cost
+            #(|2)#,location
+            #(|2)#
+            id
+            #(|1)#
+            #(|0)#,Item
+            #(|1)#
+            #(|0)#,cost
+            #(|1)#
+            #(|0)#,location
+            #(|1)#
+            #[|0]#"},
+    ))
+    .await?;
+
+    // <https://github.com/helix-editor/helix/issues/12461>
+    test((
+        indoc! {"\
+            real R〉 #(||)# 〈real R〉 @ 〈real R〉
+            #(||)# 〈real R〉 + 〈ureal R〉 i #(||)# 〈real R〉 - 〈ureal R〉 i
+            #(||)# 〈real R〉 + i #(||)# 〈real R〉 - i #(||)# 〈real R〉 〈infnan〉 i
+            #(||)# + 〈ureal R〉 i #(||)# - 〈ureal R〉 i
+            #(||)# 〈infnan〉 i #(||)# + i #[||]# - i"},
+        "i<ret>",
+        indoc! {"\
+            real R〉
+            #(||)# 〈real R〉 @ 〈real R〉
+
+            #(||)# 〈real R〉 + 〈ureal R〉 i
+            #(||)# 〈real R〉 - 〈ureal R〉 i
+
+            #(||)# 〈real R〉 + i
+            #(||)# 〈real R〉 - i
+            #(||)# 〈real R〉 〈infnan〉 i
+
+            #(||)# + 〈ureal R〉 i
+            #(||)# - 〈ureal R〉 i
+
+            #(||)# 〈infnan〉 i
+            #(||)# + i
+            #[||]# - i"},
+    ))
+    .await?;
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread")]
 async fn insert_newline_trim_trailing_whitespace() -> anyhow::Result<()> {
     // Trailing whitespace is trimmed.
@@ -117,6 +218,33 @@ async fn insert_newline_continue_line_comment() -> anyhow::Result<()> {
     ))
     .await?;
 
+    // Comment continuation should work on multiple selections.
+    // <https://github.com/helix-editor/helix/issues/12539>
+    test((
+        indoc! {"\
+            ///·Docs#[|·]#
+            pub·struct·A;
+
+            ///·Docs#(|·)#
+            pub·struct·B;
+            "}
+        .replace('·', " "),
+        ":lang rust<ret>i<ret><ret>",
+        indoc! {"\
+            ///·Docs
+            ///
+            ///·#[|·]#
+            pub·struct·A;
+
+            ///·Docs
+            ///
+            ///·#(|·)#
+            pub·struct·B;
+            "}
+        .replace('·', " "),
+    ))
+    .await?;
+
     Ok(())
 }