diff --git a/psbt/strict_tx_values_test.go b/psbt/strict_tx_values_test.go
index 83ed6bdd..e31b8be2 100644
--- a/psbt/strict_tx_values_test.go
+++ b/psbt/strict_tx_values_test.go
@@ -240,7 +240,9 @@ func TestParsesWitnessUtxoTxOutStrictly(t *testing.T) {
 		strictnessPSBTWithWitnessUtxo(t, txOutBytes),
 	), false)
 	require.NoError(t, err)
-	require.Equal(t, pkScript, packet.Inputs[0].WitnessUtxo.PkScript)
+	script := packet.Inputs[0].WitnessUtxo.PkScript
+	require.Equal(t, pkScript, script)
+	require.Equal(t, len(script), cap(script))
 
 	malformedTxOut := append(append([]byte{}, txOutBytes...), 0x00)
 	_, err = NewFromRawBytes(bytes.NewReader(
diff --git a/psbt/utils.go b/psbt/utils.go
index baf75583..9bad7722 100644
--- a/psbt/utils.go
+++ b/psbt/utils.go
@@ -315,6 +315,13 @@ func readTxOut(txout []byte) (*wire.TxOut, error) {
 		return nil, err
 	}
 
+	// wire.ReadTxOut stores PkScript in an internal 4 MiB script slab.
+	// Compact it before storing the TxOut in the PSBT so tiny witness
+	// scripts do not retain the full slab.
+	script := make([]byte, len(txOut.PkScript))
+	copy(script, txOut.PkScript)
+	txOut.PkScript = script
+
 	return txOut, nil
 }