diff --git a/src/Pstream/mpi/UPstreamRequest.C b/src/Pstream/mpi/UPstreamRequest.C
index af557cd096..55d6ef1c18 100644
--- a/src/Pstream/mpi/UPstreamRequest.C
+++ b/src/Pstream/mpi/UPstreamRequest.C
@@ -855,7 +855,7 @@ bool Foam::UPstream::finishedRequest(const label i)
     // This allows MPI to progress behind the scenes if it wishes.
 
     int flag = 0;
-    if (i < 0 || i >= PstreamGlobals::outstandingRequests_.size())
+    if (i >= 0 && i < PstreamGlobals::outstandingRequests_.size())
     {
         auto& request = PstreamGlobals::outstandingRequests_[i];