diff --git a/wallet/wallet.go b/wallet/wallet.go
index f5ab36d..8c1d21f 100644
--- a/wallet/wallet.go
+++ b/wallet/wallet.go
@@ -294,10 +294,11 @@ func (sw *SingleAddressWallet) FundTransaction(txn *types.Transaction, amount ty
 	sw.mu.Lock()
 	defer sw.mu.Unlock()
 
-	// remove locked and spent outputs
+	// remove immature, locked and spent outputs
+	cs := sw.cm.TipState()
 	utxos := make([]types.SiacoinElement, 0, len(elements))
 	for _, sce := range elements {
-		if time.Now().Before(sw.locked[sce.ID]) || tpoolSpent[sce.ID] {
+		if time.Now().Before(sw.locked[sce.ID]) || tpoolSpent[sce.ID] || cs.Index.Height < sce.MaturityHeight {
 			continue
 		}
 		utxos = append(utxos, sce.SiacoinElement)
diff --git a/wallet/wallet_test.go b/wallet/wallet_test.go
index d2ecf5e..6c1ef6b 100644
--- a/wallet/wallet_test.go
+++ b/wallet/wallet_test.go
@@ -79,10 +79,27 @@ func TestWallet(t *testing.T) {
 	}
 
 	// check that the wallet has an immature balance
-	if checkBalance(w, types.ZeroCurrency, types.ZeroCurrency, initialReward, types.ZeroCurrency); err != nil {
+	if err := checkBalance(w, types.ZeroCurrency, types.ZeroCurrency, initialReward, types.ZeroCurrency); err != nil {
 		t.Fatal(err)
 	}
 
+	// create a transaction that splits the wallet's balance into 20 outputs
+	txn := types.Transaction{
+		SiacoinOutputs: make([]types.SiacoinOutput, 20),
+	}
+	for i := range txn.SiacoinOutputs {
+		txn.SiacoinOutputs[i] = types.SiacoinOutput{
+			Value:   initialReward.Div64(20),
+			Address: w.Address(),
+		}
+	}
+
+	// try funding the transaction, expect it to fail since the outputs are immature
+	_, err = w.FundTransaction(&txn, initialReward, false)
+	if err != wallet.ErrNotEnoughFunds {
+		t.Fatal("expected ErrNotEnoughFunds, got", err)
+	}
+
 	// mine until the payout matures
 	tip := cm.TipState()
 	target := tip.MaturityHeight() + 1
@@ -94,7 +111,7 @@ func TestWallet(t *testing.T) {
 	}
 
 	// check that one payout has matured
-	if checkBalance(w, initialReward, initialReward, types.ZeroCurrency, types.ZeroCurrency); err != nil {
+	if err := checkBalance(w, initialReward, initialReward, types.ZeroCurrency, types.ZeroCurrency); err != nil {
 		t.Fatal(err)
 	}
 
@@ -116,17 +133,6 @@ func TestWallet(t *testing.T) {
 		t.Fatalf("expected miner payout, got %v", events[0].Source)
 	}
 
-	// split the wallet's balance into 20 outputs
-	txn := types.Transaction{
-		SiacoinOutputs: make([]types.SiacoinOutput, 20),
-	}
-	for i := range txn.SiacoinOutputs {
-		txn.SiacoinOutputs[i] = types.SiacoinOutput{
-			Value:   initialReward.Div64(20),
-			Address: w.Address(),
-		}
-	}
-
 	// fund and sign the transaction
 	toSign, err := w.FundTransaction(&txn, initialReward, false)
 	if err != nil {