diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
index 52a4123..ca62952 100644
--- a/hw/scsi/megasas.c
+++ b/hw/scsi/megasas.c
@@ -461,9 +461,12 @@
 {
     PCIDevice *p = PCI_DEVICE(s);
 
-    pci_dma_unmap(p, cmd->frame, cmd->pa_size, 0, 0);
+    if (cmd->pa_size) {
+        pci_dma_unmap(p, cmd->frame, cmd->pa_size, 0, 0);
+    }
     cmd->frame = NULL;
     cmd->pa = 0;
+    cmd->pa_size = 0;
     clear_bit(cmd->index, s->frame_map);
 }