diff --git a/src/libCom/osi/epicsTime.cpp b/src/libCom/osi/epicsTime.cpp
index 2fcf29a4d..c500cee08 100644
--- a/src/libCom/osi/epicsTime.cpp
+++ b/src/libCom/osi/epicsTime.cpp
@@ -255,8 +255,8 @@ epicsTime::operator time_t_wrapper () const
     time_t_wrapper wrap;
 
     if ( lti.useDiffTimeOptimization ) {
-        if ( this->secPastEpoch < ULONG_MAX - lti.epicsEpochOffset ) {
-           wrap.ts = static_cast <time_t> ( this->secPastEpoch + lti.epicsEpochOffset );
+        if ( this->secPastEpoch < ULONG_MAX - lti.epicsEpochOffsetAsAnUnsignedLong ) {
+           wrap.ts = static_cast <time_t> ( this->secPastEpoch + lti.epicsEpochOffsetAsAnUnsignedLong );
            return wrap;
        }
     }