diff --git a/polipo.go b/polipo.go
index 5eeae22..e5f0a17 100644
--- a/polipo.go
+++ b/polipo.go
@@ -17,10 +17,10 @@ type Task[T any] func() (T, error)
 // Polipo stores a list of Tasks to be run concurrently.
 type Polipo[T any] struct {
 	sync.RWMutex
-	tasks             []Task[T]
-	maxConcurrency    int
-	concurrencyBuffer chan struct{}
-	processing        bool // processing is used to prevent adding tasks while Do is running.
+	tasks             []Task[T]     // tasks is a list of Tasks to be run concurrently.
+	maxConcurrency    int           // maxConcurrency is the maximum number of concurrent tasks to run.
+	concurrencyBuffer chan struct{} // concurrencyBuffer is used to limit the number of concurrent tasks.
+	processing        bool          // processing is used to prevent adding tasks while Do is running.
 }
 
 // NewPolipo creates a new Polipo. It accepts options to configure the Polipo.
@@ -65,6 +65,10 @@ func (p *Polipo[T]) AddTask(task Task[T]) error {
 // set by passing `WithMaxConcurrency` as an option. The default is 10.
 // This is a blocking function that will return when all the Tasks have finished their work.
 func (p *Polipo[T]) Do(ctx context.Context) ([]T, error) {
+	if len(p.tasks) == 0 {
+		return nil, errors.New("no tasks to do")
+	}
+
 	if p.processing {
 		return nil, errors.New("already processing tasks")
 	}
@@ -77,11 +81,7 @@ func (p *Polipo[T]) Do(ctx context.Context) ([]T, error) {
 
 	p.processing = true
 
-	if len(p.tasks) == 0 {
-		return nil, errors.New("no tasks to do")
-	}
-
-	resultsChan := make(chan result[T])
+	processedChan := make(chan processed[T])
 	wg := sync.WaitGroup{}
 
 	wg.Add(len(p.tasks))
@@ -94,10 +94,10 @@ func (p *Polipo[T]) Do(ctx context.Context) ([]T, error) {
 
 			go func(t Task[T]) {
 				defer wg.Done()
-				items, err := t()
+				result, err := t()
 
 				select {
-				case resultsChan <- result[T]{items, err}:
+				case processedChan <- processed[T]{result, err}:
 				case <-ctx.Done():
 				}
 
@@ -110,7 +110,7 @@ func (p *Polipo[T]) Do(ctx context.Context) ([]T, error) {
 	// Wait for all tasks to finish.
 	go func() {
 		wg.Wait()
-		close(resultsChan)
+		close(processedChan)
 	}()
 
 	var (
@@ -127,24 +127,23 @@ func (p *Polipo[T]) Do(ctx context.Context) ([]T, error) {
 		}
 
 		select {
-		case res, ok := <-resultsChan:
+		case r, ok := <-processedChan:
 			if !ok {
 				return results, errors.Join(errs...)
 			}
 
-			if res.err != nil {
-				errs = append(errs, res.err)
-				continue
+			if r.err != nil {
+				errs = append(errs, r.err)
 			}
 
-			results = append(results, res.resp)
+			results = append(results, r.result)
 		case <-ctx.Done():
 			return results, errors.Join(append(errs, ctx.Err())...)
 		}
 	}
 }
 
-type result[T any] struct {
-	resp T
-	err  error
+type processed[T any] struct {
+	result T
+	err    error
 }
diff --git a/polipo_test.go b/polipo_test.go
index d911336..3b3d662 100644
--- a/polipo_test.go
+++ b/polipo_test.go
@@ -132,7 +132,7 @@ func TestPolipo_Do(t *testing.T) {
 
 		allResults, err := p.Do(ctx)
 		require.ErrorContains(t, err, "nothing in the ocean")
-		require.Len(t, allResults, 1)
+		require.Len(t, allResults, 2)
 		require.ElementsMatch(t, []TaskResult{
 			{
 				Fishes: []string{
@@ -140,6 +140,9 @@ func TestPolipo_Do(t *testing.T) {
 					"Marlin",
 				},
 			},
+			{
+				Fishes: nil,
+			},
 		}, allResults)
 	})
 
@@ -194,6 +197,45 @@ func TestPolipo_Do(t *testing.T) {
 			},
 		}, allResults)
 	})
+
+	t.Run("adding tasks should return an error if already processing", func(t *testing.T) {
+		ctx := context.TODO()
+
+		p := polipo.NewPolipo[TaskResult]()
+
+		err := p.AddTask(func() (TaskResult, error) {
+			time.Sleep(time.Second)
+
+			return TaskResult{}, nil
+		})
+		require.NoError(t, err)
+
+		go func() {
+			_, _ = p.Do(ctx)
+		}()
+
+		time.Sleep(time.Millisecond * 100)
+
+		err = p.AddTask(func() (TaskResult, error) {
+			return TaskResult{
+				Fishes: []string{
+					"Salmon",
+					"Tuna",
+				},
+			}, nil
+		})
+		require.ErrorContains(t, err, "cannot add tasks while processing")
+	})
+
+	t.Run("should return an error if no tasks to do", func(t *testing.T) {
+		ctx := context.TODO()
+
+		p := polipo.NewPolipo[TaskResult]()
+
+		allResults, err := p.Do(ctx)
+		require.ErrorContains(t, err, "no tasks to do")
+		require.Empty(t, allResults)
+	})
 }
 
 var testCases = []struct {