diff --git a/src/sys/device.c b/src/sys/device.c
index ffff8864..4f3d697c 100644
--- a/src/sys/device.c
+++ b/src/sys/device.c
@@ -631,7 +631,7 @@ PVOID FspFsvolDeviceEnumerateContextByName(PDEVICE_OBJECT DeviceObject, PUNICODE
         0, 0, NextFlag, &RestartKey->RestartKey, &RestartKey->DeleteCount, &FileName);
 
     if (0 != Result &&
-        RtlPrefixUnicodeString(FileName, Result->FileName, CaseInsensitive) &&
+        FspFileNameIsPrefix(FileName, Result->FileName, CaseInsensitive, 0) &&
         FileName->Length < Result->FileName->Length &&
         '\\' == Result->FileName->Buffer[FileName->Length / sizeof(WCHAR)])
         return Result->Context;
@@ -699,7 +699,7 @@ static RTL_GENERIC_COMPARE_RESULTS NTAPI FspFsvolDeviceCompareContextByName(
     PUNICODE_STRING SecondFileName = *(PUNICODE_STRING *)SecondElement;
     LONG ComparisonResult;
 
-    ComparisonResult = RtlCompareUnicodeString(FirstFileName, SecondFileName, CaseInsensitive);
+    ComparisonResult = FspFileNameCompare(FirstFileName, SecondFileName, CaseInsensitive, 0);
 
     if (0 > ComparisonResult)
         return GenericLessThan;
diff --git a/src/sys/driver.h b/src/sys/driver.h
index 4b326905..4d05055f 100644
--- a/src/sys/driver.h
+++ b/src/sys/driver.h
@@ -436,6 +436,21 @@ enum
 BOOLEAN FspFileNameIsValid(PUNICODE_STRING Path, PUNICODE_STRING StreamPart, PULONG StreamType);
 BOOLEAN FspFileNameIsValidPattern(PUNICODE_STRING Pattern);
 VOID FspFileNameSuffix(PUNICODE_STRING Path, PUNICODE_STRING Remain, PUNICODE_STRING Suffix);
+#if 0
+LONG FspFileNameCompare(
+    PUNICODE_STRING Name1,
+    PUNICODE_STRING Name2,
+    BOOLEAN IgnoreCase,
+    PCWCH UpcaseTable);
+BOOLEAN FspFileNameIsPrefix(
+    PCUNICODE_STRING Name1,
+    PCUNICODE_STRING Name2,
+    BOOLEAN IgnoreCase,
+    PCWCH UpcaseTable);
+#else
+#define FspFileNameCompare(N1,N2,I,U)   (ASSERT(0 == (U)), RtlCompareUnicodeString(N1,N2,I))
+#define FspFileNameIsPrefix(N1,N2,I,U)  (ASSERT(0 == (U)), RtlPrefixUnicodeString(N1,N2,I))
+#endif
 NTSTATUS FspFileNameInExpression(
     PUNICODE_STRING Expression,
     PUNICODE_STRING Name,
diff --git a/src/sys/name.c b/src/sys/name.c
index 0c9d38ca..45ecc2b6 100644
--- a/src/sys/name.c
+++ b/src/sys/name.c
@@ -211,6 +211,9 @@ NTSTATUS FspFileNameInExpression(
 {
     PAGED_CODE();
 
+    /* we do not support non-NULL UpcaseTable yet */
+    ASSERT(0 == UpcaseTable);
+
     try
     {
         *PResult = FsRtlIsNameInExpression(Expression, Name, IgnoreCase, UpcaseTable);