diff --git a/LSL2/STPROC/RDS_SERVICES.txt b/LSL2/STPROC/RDS_SERVICES.txt
index 80f4a5f..f4e4ee9 100644
--- a/LSL2/STPROC/RDS_SERVICES.txt
+++ b/LSL2/STPROC/RDS_SERVICES.txt
@@ -809,7 +809,7 @@ Service IsTWLoggingReqd(RDSNo)
                 Layer = Field(PRSPropKey, '*', 2)
                 MeasureFreq = PRSPropRec<PRS_PROP_FREQ$>
                 Start = PRSPropRec<PRS_PROP_MET_START$>
-                If WaferType NE 'Product' AND WaferType NE 'Prod' then
+                If WaferType NE 'Product' AND WaferType NE 'Prod' AND WaferType NE '' then
                     BEGIN CASE
                         CASE MeasureFreq = 'F' AND ThisReactorRunOrder = 1	; IsTWReqd = 1
                         CASE ThisReactorRunOrder = Start					; IsTWReqd = 1
@@ -1828,3 +1828,4 @@ return
 
 
 
+