diff --git a/reactos/lib/rtl/unicode.c b/reactos/lib/rtl/unicode.c
index 2089c5d26c6..b9b9586dfea 100644
--- a/reactos/lib/rtl/unicode.c
+++ b/reactos/lib/rtl/unicode.c
@@ -1632,7 +1632,7 @@ RtlUpcaseUnicodeStringToCountedOemString(
         OemDest->MaximumLength = Length;
         if (!OemDest->Buffer) return STATUS_NO_MEMORY;
     }
-    else if (OemDest->Length >= OemDest->MaximumLength)
+    else if (OemDest->Length > OemDest->MaximumLength)
     {
         return STATUS_BUFFER_OVERFLOW;
     }