diff --git a/50-main.config b/50-main.config
index a59ec4e..c16798e 100644
--- a/50-main.config
+++ b/50-main.config
@@ -66,7 +66,7 @@ START = (time() < GLIDEIN_ToRetire) && \
         ((DESIRED_Sites=?=undefined) || stringListMember(GLIDEIN_Site,DESIRED_Sites,",")) && \
         ((UNDESIRED_Sites=?=undefined) || !stringListMember(GLIDEIN_Site,UNDESIRED_Sites,",")) && \
         (!isUndefined(TARGET.ProjectName)) && \
-        (MY.GPUs is Undefined || MY.GPUs == 0 || \
+        ((MY.GPUs ?: 0) == 0 || \
            (TARGET.RequestGPUs ?: 0) > 0 || \
            RoomForCPUOnlyJobs is Undefined || RoomForCPUOnlyJobs) && \
         (isUndefined(TARGET.SingularityImage) || MY.SINGULARITY_START_CLAUSE) && \