diff --git a/crates/diagnostics/src/build_log.rs b/crates/diagnostics/src/build_log.rs
index 1234567..abcdefg 100644
--- a/crates/diagnostics/src/build_log.rs
+++ b/crates/diagnostics/src/build_log.rs
@@ -14,8 +14,13 @@ pub fn update(
 
     let data = log_document.data.as_log()?;
 
-    let parents = deps::parents(workspace, log_document);
-    let root_document = parents.iter().next()?;
+    // Try to find the compiled .tex file from the log file name first.
+    // This handles subfile compilation where the subfile is the actual root.
+    let root_document = find_compiled_document(workspace, log_document)
+        .or_else(|| {
+            // Fallback to original behavior: find parent via dependency graph
+            deps::parents(workspace, log_document).into_iter().next()
+        })?;
 
     let base_path = root_document
         .path
@@ -57,3 +62,14 @@ fn find_range_of_hint(document: &Document, error: &BuildError) -> Option<TextRan
     let hint_end = hint_start + hint.text_len();
     Some(TextRange::new(hint_start, hint_end))
 }
+
+/// Given a .log file, find the corresponding .tex file that was compiled.
+/// E.g., `/path/to/chapter.log` -> `/path/to/chapter.tex`
+fn find_compiled_document<'a>(
+    workspace: &'a Workspace,
+    log_document: &Document,
+) -> Option<&'a Document> {
+    let log_path = log_document.path.as_ref()?;
+    let tex_path = log_path.with_extension("tex");
+    let tex_uri = Url::from_file_path(&tex_path).ok()?;
+    workspace.lookup(&tex_uri)
+}