diff --git a/internal/conversion/worker_test.go b/internal/conversion/worker_test.go
index 9b2cab58..37894b64 100644
--- a/internal/conversion/worker_test.go
+++ b/internal/conversion/worker_test.go
@@ -687,3 +687,38 @@ func TestConvertOperation_InvalidStorageFormat(t *testing.T) {
 	assert.Error(t, err)
 	assert.Contains(t, err.Error(), "get storage engine")
 }
+
+func TestConvertOperation_JSONFileNotFound(t *testing.T) {
+	dir := t.TempDir()
+	// Don't create the JSON file - test the "file not found" error path
+
+	repo := newErrorMockRepo()
+	worker := NewWorker(repo, Config{
+		DataDir: dir,
+	})
+
+	ctx := context.Background()
+	err := worker.ConvertOne(ctx, 1, "nonexistent")
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "JSON file not found")
+}
+
+func TestTriggerConversion_FailedStatusUpdateError(t *testing.T) {
+	dir := t.TempDir()
+	// Don't create the JSON file - will fail and try to update status to "failed"
+
+	repo := newErrorMockRepo()
+	// Make status updates fail after the initial "converting" update
+	repo.updateStatusErr = fmt.Errorf("status update failed")
+
+	worker := NewWorker(repo, Config{
+		DataDir: dir,
+	})
+
+	// TriggerConversion is async, just verify it doesn't panic
+	worker.TriggerConversion(1, "nonexistent")
+
+	// Give the goroutine time to run
+	time.Sleep(100 * time.Millisecond)
+}
diff --git a/internal/server/marker_test.go b/internal/server/marker_test.go
index de0db48a..d739b75f 100644
--- a/internal/server/marker_test.go
+++ b/internal/server/marker_test.go
@@ -424,6 +424,32 @@ func TestScanDir(t *testing.T) {
 	})
 }
 
+func TestPaintSVG_InvalidTemplate(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create SVG with invalid template syntax
+	invalidPath := filepath.Join(dir, "invalid.svg")
+	err := os.WriteFile(invalidPath, []byte(`<svg>{{ .Unclosed`), 0644)
+	require.NoError(t, err)
+
+	c := color.RGBA{255, 0, 0, 255}
+	_, err = paintSVG(invalidPath, c)
+	assert.Error(t, err)
+}
+
+func TestPaintPNG_InvalidImage(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create file with .png extension but invalid image data
+	invalidPath := filepath.Join(dir, "invalid.png")
+	err := os.WriteFile(invalidPath, []byte("not a valid png"), 0644)
+	require.NoError(t, err)
+
+	c := color.RGBA{255, 0, 0, 255}
+	_, err = paintPNG(invalidPath, c)
+	assert.Error(t, err)
+}
+
 func TestMax(t *testing.T) {
 	tests := []struct {
 		a, b, want uint8