diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8045b203..80f169bf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased
 
 - Skip unchanged issue-comment downloads on issues and PRs using parent timestamps, comment counts, and completed saved observations; keep PR review and detail data live, and add `sync`/`refresh --force` for a full selected refresh. Thanks @vlsi for the report.
+- Order captured comments chronologically when source timestamps have different fractional-second precision, preserving deterministic ties by kind and stable ID.
 
 ## 0.10.0 - 2026-09-13
 
diff --git a/docs/capture.md b/docs/capture.md
index e24f4a0a..6e53e3a4 100644
--- a/docs/capture.md
+++ b/docs/capture.md
@@ -71,6 +71,8 @@ The top-level object contains:
 Each thread contains its stable GitHub ID, number, kind, state, title, body,
 author, URL, labels, assignees, timestamps, comments, and semantic
 `content_hash`. Comments are ordered by source time, kind, and stable ID.
+Source times are compared chronologically, including fractional seconds and
+timezone offsets. Comments without a source time sort first.
 
 The semantic hash covers the exported thread before `content_hash` is set. It
 changes when exported thread or comment content changes.
diff --git a/internal/capture/capture.go b/internal/capture/capture.go
index bc7381ee..96bd1f8e 100644
--- a/internal/capture/capture.go
+++ b/internal/capture/capture.go
@@ -359,7 +359,14 @@ func buildThread(
 	}
 	sort.Slice(capturedComments, func(left, right int) bool {
 		if capturedComments[left].CreatedAt != capturedComments[right].CreatedAt {
-			return capturedComments[left].CreatedAt < capturedComments[right].CreatedAt
+			leftCreated, rightCreated := capturedComments[left].CreatedAt, capturedComments[right].CreatedAt
+			if leftCreated == "" || rightCreated == "" {
+				return leftCreated == ""
+			}
+			// Validated RFC3339Nano strings are not ordered by fractional-second precision.
+			leftTime, _ := time.Parse(time.RFC3339Nano, leftCreated)
+			rightTime, _ := time.Parse(time.RFC3339Nano, rightCreated)
+			return leftTime.Before(rightTime)
 		}
 		if capturedComments[left].Kind != capturedComments[right].Kind {
 			return capturedComments[left].Kind < capturedComments[right].Kind
diff --git a/internal/capture/comment_order_test.go b/internal/capture/comment_order_test.go
new file mode 100644
index 00000000..75823e6a
--- /dev/null
+++ b/internal/capture/comment_order_test.go
@@ -0,0 +1,61 @@
+package capture
+
+import (
+	"context"
+	"path/filepath"
+	"slices"
+	"testing"
+
+	"github.com/openclaw/gitcrawl/internal/store"
+)
+
+func TestBuildThreadOrdersCommentsByInstant(t *testing.T) {
+	ctx := context.Background()
+	st, err := store.Open(ctx, filepath.Join(t.TempDir(), "archive.db"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer st.Close()
+	repoID, err := st.UpsertRepository(ctx, store.Repository{
+		Owner: "example", Name: "archive", FullName: "example/archive", UpdatedAt: "2026-09-15T00:00:01Z",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	thread := store.Thread{
+		RepoID: repoID, GitHubID: "1", Number: 1, Kind: "pull_request", State: "open",
+		Title: "Synthetic conversation", LabelsJSON: "[]", AssigneesJSON: "[]", RawJSON: "{}",
+		UpdatedAtGitHub: "2026-09-15T00:00:01Z", UpdatedAt: "2026-09-15T00:00:01Z",
+	}
+	thread.ID, err = st.UpsertThread(ctx, thread)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, comment := range []store.Comment{
+		{GitHubID: "missing", CommentType: "issue_comment"},
+		{GitHubID: "whole", CommentType: "issue_comment", CreatedAtGitHub: "2026-09-15T00:00:00Z"},
+		{GitHubID: "tenth", CommentType: "issue_comment", CreatedAtGitHub: "2026-09-15T00:00:00.1Z"},
+		{GitHubID: "later", CommentType: "issue_comment", CreatedAtGitHub: "2026-09-15T00:00:00.11Z"},
+		{GitHubID: "nano", CommentType: "issue_comment", CreatedAtGitHub: "2026-09-15T00:00:00.000000001Z"},
+		{GitHubID: "review", CommentType: "pull_review", CreatedAtGitHub: "2026-09-15T01:00:00.1+01:00"},
+		{GitHubID: "a-tenth", CommentType: "issue_comment", CreatedAtGitHub: "2026-09-15T00:00:00.100Z"},
+	} {
+		comment.ThreadID, comment.RawJSON = thread.ID, "{}"
+		if _, err := st.UpsertComment(ctx, comment); err != nil {
+			t.Fatal(err)
+		}
+	}
+	reserveComments(t, ctx, st, thread.ID, thread.UpdatedAtGitHub)
+	got, err := buildThread(ctx, st, thread)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var ids []string
+	for _, comment := range got.Comments {
+		ids = append(ids, comment.ID)
+	}
+	want := []string{"missing", "whole", "nano", "a-tenth", "tenth", "review", "later"}
+	if !slices.Equal(ids, want) {
+		t.Fatalf("comment order = %v, want %v", ids, want)
+	}
+}