diff --git a/actions-languageservice/src/utils/transform.test.ts b/actions-languageservice/src/utils/transform.test.ts
new file mode 100644
index 0000000..e9b2339
--- /dev/null
+++ b/actions-languageservice/src/utils/transform.test.ts
@@ -0,0 +1,47 @@
+import {getPositionFromCursor} from "../test-utils/cursor-position";
+import {transform} from "./transform";
+
+describe("transform", () => {
+  it("adds : at end of line", () => {
+    const [doc, pos] = getPositionFromCursor("on: push\njobs:\n  build:\n    runs-on|");
+    const [newDoc, newPos] = transform(doc, pos);
+
+    expect(newDoc.getText()).toEqual(`on: push
+jobs:
+  build:
+    runs-on:`);
+    expect(newPos.character).toEqual(11);
+  });
+
+  it("adds placeholder node in empty sequence", () => {
+    const [doc, pos] = getPositionFromCursor(`on: push
+jobs:
+  build:
+    runs-on:
+      - |`);
+    const [newDoc, newPos] = transform(doc, pos);
+
+    expect(newDoc.getText()).toEqual(`on: push
+jobs:
+  build:
+    runs-on:
+      - dummy`);
+    expect(newPos.character).toEqual(9);
+  });
+
+  it("adds placeholder node in empty line", () => {
+    const [doc, pos] = getPositionFromCursor(`on: push
+jobs:
+  build:
+    runs-on:
+      |`);
+    const [newDoc, newPos] = transform(doc, pos);
+
+    expect(newDoc.getText()).toEqual(`on: push
+jobs:
+  build:
+    runs-on:
+      dummy:`);
+    expect(newPos.character).toEqual(7);
+  });
+});
diff --git a/actions-languageservice/src/utils/transform.ts b/actions-languageservice/src/utils/transform.ts
index 35fb54d..4b45798 100644
--- a/actions-languageservice/src/utils/transform.ts
+++ b/actions-languageservice/src/utils/transform.ts
@@ -5,16 +5,12 @@ const DUMMY_KEY = "dummy";
 // Transform a document to work around YAML parsing issues
 // Based on `_transform` in https://github.com/cschleiden/github-actions-parser/blob/main/src/lib/parser/complete.ts#L311
 export function transform(doc: TextDocument, pos: Position): [TextDocument, Position] {
-  const input = doc.getText();
   let offset = doc.offsetAt(pos);
-  // TODO: Optimize this...
-  const lines = input.split("\n");
-  const lineNo = input
-    .substring(0, offset)
-    .split("")
-    .filter(x => x === "\n").length;
-  const linePos = offset - lines.slice(0, lineNo).reduce((p, l) => p + l.length + 1, 0);
-  const line = lines[lineNo];
+  let line = doc.getText({
+    start: {line: pos.line, character: 0},
+    end: {line: pos.line, character: Number.MAX_SAFE_INTEGER}
+  });
+  const linePos = pos.character;
 
   let partialInput = line.trim();
   // Special case for Actions, if this line contains an expression marker, do _not_ transform. This is
@@ -32,24 +28,32 @@ export function transform(doc: TextDocument, pos: Position): [TextDocument, Posi
           offset++;
         }
 
-        lines[lineNo] =
+        line =
           line.substring(0, linePos) + spacer + DUMMY_KEY + (trimmedLine === "-" ? "" : ":") + line.substring(linePos);
 
         // Adjust pos by one to prevent a sequence node being marked as active
         offset++;
       } else if (!trimmedLine.startsWith("-")) {
         // Add `:` to end of line
-        lines[lineNo] = line + ":";
-      }
-
-      if (trimmedLine.startsWith("-")) {
-        partialInput = trimmedLine.substring(trimmedLine.indexOf("-") + 1).trim();
+        line = line + ":";
       }
     } else {
-      partialInput = (offset > colon ? line.substring(colon + 1) : line.substring(0, colon)).trim();
       offset = offset - 1;
     }
   }
-  const newDoc = TextDocument.create(doc.uri, doc.languageId, doc.version, lines.join("\n"));
+
+  const newDoc = TextDocument.create(doc.uri, doc.languageId, doc.version, doc.getText());
+
+  TextDocument.update(
+    newDoc,
+    [
+      {
+        range: {start: {line: pos.line, character: 0}, end: {line: pos.line, character: Number.MAX_SAFE_INTEGER}},
+        text: line
+      }
+    ],
+    newDoc.version + 1
+  );
+
   return [newDoc, newDoc.positionAt(offset)];
 }