diff --git a/Cargo.lock b/Cargo.lock
index 6f0b1514..b0ad29a9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1428,6 +1428,7 @@ dependencies = [
  "fs4",
  "home",
  "indexmap",
+ "line-index",
  "log",
  "petgraph",
  "schemars",
diff --git a/crates/moonbuild/src/expect.rs b/crates/moonbuild/src/expect.rs
index 19e268f5..0e7a6271 100644
--- a/crates/moonbuild/src/expect.rs
+++ b/crates/moonbuild/src/expect.rs
@@ -18,6 +18,7 @@
 
 use anyhow::Context;
 use colored::Colorize;
+use moonutil::common::line_col_to_byte_idx;
 use std::collections::BTreeSet;
 use std::collections::HashMap;
 use std::path::PathBuf;
@@ -217,14 +218,6 @@ impl Replace {
     }
 }
 
-fn line_col_to_byte_idx(line_index: &line_index::LineIndex, line: u32, col: u32) -> Option<usize> {
-    let offset = line_index.offset(line_index.to_utf8(
-        line_index::WideEncoding::Utf32,
-        line_index::WideLineCol { line, col },
-    )?)?;
-    Some(usize::from(offset))
-}
-
 fn parse_expect_failed_message(msg: &str) -> anyhow::Result<Replace> {
     let j: ExpectFailedRaw = serde_json_lenient::from_str(msg)
         .context(format!("parse expect test result failed: {}", msg))?;
diff --git a/crates/moonutil/Cargo.toml b/crates/moonutil/Cargo.toml
index ac6c9d4f..ac956855 100644
--- a/crates/moonutil/Cargo.toml
+++ b/crates/moonutil/Cargo.toml
@@ -44,6 +44,7 @@ env_logger.workspace = true
 log.workspace = true
 thiserror.workspace = true
 schemars.workspace = true
+line-index.workspace = true
 
 [dev-dependencies]
 expect-test.workspace = true
diff --git a/crates/moonutil/src/common.rs b/crates/moonutil/src/common.rs
index 6f7aba9d..0006ec73 100644
--- a/crates/moonutil/src/common.rs
+++ b/crates/moonutil/src/common.rs
@@ -785,3 +785,15 @@ impl MooncGenTestInfo {
         result
     }
 }
+
+pub fn line_col_to_byte_idx(
+    line_index: &line_index::LineIndex,
+    line: u32,
+    col: u32,
+) -> Option<usize> {
+    let offset = line_index.offset(line_index.to_utf8(
+        line_index::WideEncoding::Utf32,
+        line_index::WideLineCol { line, col },
+    )?)?;
+    Some(usize::from(offset))
+}
diff --git a/crates/moonutil/src/render.rs b/crates/moonutil/src/render.rs
index 2748358f..a16af257 100644
--- a/crates/moonutil/src/render.rs
+++ b/crates/moonutil/src/render.rs
@@ -19,6 +19,8 @@
 use ariadne::Fmt;
 use serde::{Deserialize, Serialize};
 
+use crate::common::line_col_to_byte_idx;
+
 #[derive(Debug, Serialize, Deserialize)]
 pub struct MooncDiagnostic {
     pub level: String,
@@ -43,24 +45,16 @@ pub struct Position {
 
 impl Position {
     pub fn calculate_offset(&self, content: &str) -> usize {
-        // line and col count from 1
-        let mut current_line = 1;
-        let mut current_col = 1;
-
-        for (char_idx, (_, c)) in content.char_indices().enumerate() {
-            if current_line == self.line && current_col == self.col {
-                return char_idx;
-            }
-
-            if c == '\n' {
-                current_line += 1;
-                current_col = 1;
-            } else {
-                current_col += 1;
-            }
-        }
+        let line_index = line_index::LineIndex::new(content);
+        let byte_based_index =
+            line_col_to_byte_idx(&line_index, self.line as u32 - 1, self.col as u32 - 1).unwrap();
 
-        content.chars().count()
+        content
+            .char_indices()
+            .enumerate()
+            .find(|(_, (byte_offset, _))| *byte_offset == byte_based_index)
+            .map(|(i, _)| i)
+            .unwrap_or(usize::from(line_index.len()))
     }
 }