diff --git a/src/add-ons/kernel/busses/scsi/ahci/ahci_port.cpp b/src/add-ons/kernel/busses/scsi/ahci/ahci_port.cpp
index 3a5611d529..00f17ebfae 100644
--- a/src/add-ons/kernel/busses/scsi/ahci/ahci_port.cpp
+++ b/src/add-ons/kernel/busses/scsi/ahci/ahci_port.cpp
@@ -837,12 +837,14 @@ AHCIPort::ScsiUnmap(scsi_ccb* request, scsi_unmap_parameter_list* unmapBlocks)
 			lbaRanges[i++] = B_HOST_TO_LENDIAN_INT64(
 				((uint64)blocks << 48) | lba);
 			lba += blocks;
+			bytesLeft -= blocks;
 		}
 	}
 
 	sata_request sreq;
 	sreq.set_ata48_cmd(ATA_COMMAND_DATA_SET_MANAGEMENT, 0,
 		(lbaRangesSize + 511) / 512);
+	sreq.SetFeature(1);
 	sreq.set_data(lbaRanges, lbaRangesSize);
 
 	ExecuteSataRequest(&sreq);
diff --git a/src/add-ons/kernel/busses/scsi/ahci/sata_request.cpp b/src/add-ons/kernel/busses/scsi/ahci/sata_request.cpp
index d5cfd823cc..2fe8b214e2 100644
--- a/src/add-ons/kernel/busses/scsi/ahci/sata_request.cpp
+++ b/src/add-ons/kernel/busses/scsi/ahci/sata_request.cpp
@@ -94,6 +94,14 @@ sata_request::set_ata48_cmd(uint8 command, uint64 lba, uint16 sectorCount)
 }
 
 
+void
+sata_request::SetFeature(uint16 feature)
+{
+	fFis[3] = (uint8)(feature & 0xff);
+	fFis[11] = (uint8)(feature >> 8);
+}
+
+
 void
 sata_request::set_atapi_cmd(size_t transferLength)
 {
diff --git a/src/add-ons/kernel/busses/scsi/ahci/sata_request.h b/src/add-ons/kernel/busses/scsi/ahci/sata_request.h
index 71550f6886..61191be9d1 100644
--- a/src/add-ons/kernel/busses/scsi/ahci/sata_request.h
+++ b/src/add-ons/kernel/busses/scsi/ahci/sata_request.h
@@ -20,6 +20,7 @@ public:
 	void			set_ata_cmd(uint8 command);
 	void			set_ata28_cmd(uint8 command, uint32 lba, uint8 sectorCount);
 	void			set_ata48_cmd(uint8 command, uint64 lba, uint16 sectorCount);
+	void			SetFeature(uint16 feature);
 
 	void			set_atapi_cmd(size_t transferLength);
 	bool 			is_atapi();