diff --git a/inc/winfsp/fsctl.h b/inc/winfsp/fsctl.h
index 38a1cd4e..8f9e737f 100644
--- a/inc/winfsp/fsctl.h
+++ b/inc/winfsp/fsctl.h
@@ -46,8 +46,8 @@ extern const __declspec(selectany) GUID FspFsvrtDeviceClassGuid =
 /* volume/file metadata */
 typedef struct
 {
-    UINT64 TotalAllocationUnits;
-    UINT64 AvailableAllocationUnits;
+    UINT64 TotalSize;
+    UINT64 FreeSize;
     UINT64 VolumeCreationTime;
     UINT16 VolumeLabelLength;
     WCHAR VolumeLabel[32];
diff --git a/src/sys/volinfo.c b/src/sys/volinfo.c
index b751b6c4..cd882ffb 100644
--- a/src/sys/volinfo.c
+++ b/src/sys/volinfo.c
@@ -123,10 +123,12 @@ static NTSTATUS FspFsvolQueryFsFullSizeInformation(
 
     FSP_FSVOL_DEVICE_EXTENSION *FsvolDeviceExtension = FspFsvolDeviceExtension(FsvolDeviceObject);
     PFILE_FS_FULL_SIZE_INFORMATION Info = (PFILE_FS_FULL_SIZE_INFORMATION)*PBuffer;
+    UINT64 AllocationUnit = FsvolDeviceExtension->VolumeParams.SectorSize *
+        FsvolDeviceExtension->VolumeParams.SectorsPerAllocationUnit;
 
-    Info->TotalAllocationUnits.QuadPart = VolumeInfo->TotalAllocationUnits;
-    Info->CallerAvailableAllocationUnits.QuadPart = VolumeInfo->AvailableAllocationUnits;
-    Info->ActualAvailableAllocationUnits.QuadPart = VolumeInfo->AvailableAllocationUnits;
+    Info->TotalAllocationUnits.QuadPart = VolumeInfo->TotalSize / AllocationUnit;
+    Info->CallerAvailableAllocationUnits.QuadPart =
+    Info->ActualAvailableAllocationUnits.QuadPart = VolumeInfo->FreeSize / AllocationUnit;
     Info->SectorsPerAllocationUnit = FsvolDeviceExtension->VolumeParams.SectorsPerAllocationUnit;
     Info->BytesPerSector = FsvolDeviceExtension->VolumeParams.SectorSize;
 
@@ -148,9 +150,11 @@ static NTSTATUS FspFsvolQueryFsSizeInformation(
 
     FSP_FSVOL_DEVICE_EXTENSION *FsvolDeviceExtension = FspFsvolDeviceExtension(FsvolDeviceObject);
     PFILE_FS_SIZE_INFORMATION Info = (PFILE_FS_SIZE_INFORMATION)*PBuffer;
+    UINT64 AllocationUnit = FsvolDeviceExtension->VolumeParams.SectorSize *
+        FsvolDeviceExtension->VolumeParams.SectorsPerAllocationUnit;
 
-    Info->TotalAllocationUnits.QuadPart = VolumeInfo->TotalAllocationUnits;
-    Info->AvailableAllocationUnits.QuadPart = VolumeInfo->AvailableAllocationUnits;
+    Info->TotalAllocationUnits.QuadPart = VolumeInfo->TotalSize / AllocationUnit;
+    Info->AvailableAllocationUnits.QuadPart = VolumeInfo->FreeSize / AllocationUnit;
     Info->SectorsPerAllocationUnit = FsvolDeviceExtension->VolumeParams.SectorsPerAllocationUnit;
     Info->BytesPerSector = FsvolDeviceExtension->VolumeParams.SectorSize;
 
diff --git a/tst/winfsp-tests/memfs.cpp b/tst/winfsp-tests/memfs.cpp
index 400e218b..5cc74c2e 100644
--- a/tst/winfsp-tests/memfs.cpp
+++ b/tst/winfsp-tests/memfs.cpp
@@ -194,15 +194,14 @@ static NTSTATUS GetVolumeInfo(FSP_FILE_SYSTEM *FileSystem,
 {
     MEMFS *Memfs = (MEMFS *)FileSystem->UserContext;
     MEMFS_FILE_NODE *RootNode;
-    ULONG AllocationUnits = Memfs->MaxFileSize / (MEMFS_SECTOR_SIZE * MEMFS_SECTORS_PER_ALLOCATION_UNIT);
 
     RootNode = MemfsFileNodeMapGet(Memfs->FileNodeMap, L"");
     if (0 == RootNode)
         return STATUS_DISK_CORRUPT_ERROR;
 
-    VolumeInfo->TotalAllocationUnits = Memfs->MaxFileNodes * AllocationUnits;
-    VolumeInfo->AvailableAllocationUnits =
-        (Memfs->MaxFileNodes - MemfsFileNodeMapCount(Memfs->FileNodeMap)) * AllocationUnits;
+    VolumeInfo->TotalSize = Memfs->MaxFileNodes * Memfs->MaxFileSize;
+    VolumeInfo->FreeSize =
+        (Memfs->MaxFileNodes - MemfsFileNodeMapCount(Memfs->FileNodeMap)) * Memfs->MaxFileSize;
     VolumeInfo->VolumeCreationTime = RootNode->FileInfo.CreationTime;
     VolumeInfo->VolumeLabelLength = sizeof L"MEMFS" - sizeof(WCHAR);
     memcpy(VolumeInfo->VolumeLabel, L"MEMFS", VolumeInfo->VolumeLabelLength);