diff --git a/src/OpenFOAM/global/argList/argList.C b/src/OpenFOAM/global/argList/argList.C
index e47fb46342..68a67b2c09 100644
--- a/src/OpenFOAM/global/argList/argList.C
+++ b/src/OpenFOAM/global/argList/argList.C
@@ -1690,15 +1690,26 @@ void Foam::argList::parse
                 )
                 {
                     label nProcDirs = 0;
-                    while
-                    (
-                        isDir
+                    {
+                        const bool oldParRun(UPstream::parRun(false));
+                        // Don't cache processor directories (probably not
+                        // needed since master-only
+                        const int oldCacheLevel(fileOperation::cacheLevel(0));
+                        // Accept any processorsXXX
+                        const int oldFilter(fileOperation::nProcsFilter(0));
+
+                        nProcDirs = fileHandler().nProcs
                         (
-                            rootPath_/globalCase_
-                          / ("processor" + Foam::name(++nProcDirs))
-                        )
-                    )
-                    {}
+                            rootPath_/globalCase_,
+                            "",
+                            dictNProcs  // expected nProcs
+                        );
+
+                        fileOperation::nProcsFilter(oldFilter);
+                        fileOperation::cacheLevel(oldCacheLevel);
+                        UPstream::parRun(oldParRun);
+                    }
+
 
                     if (nProcDirs != Pstream::nProcs())
                     {
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
index e10ea04e44..8addedf1d5 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
@@ -1290,7 +1290,8 @@ Foam::fileNameList Foam::fileOperation::readObjects
 Foam::label Foam::fileOperation::nProcs
 (
     const fileName& dir,
-    const fileName& local
+    const fileName& local,
+    const label wanted      // expected nProcs. 0 if not supplied
 ) const
 {
     label nProcs = 0;
@@ -1298,6 +1299,25 @@ Foam::label Foam::fileOperation::nProcs
     {
         fileNameList dirNames(Foam::readDir(dir, fileName::Type::DIRECTORY));
 
+        // E.g. (maybe left over)
+        // processor0
+        // processor1
+        // processors5
+        // processor90     // gap!
+        // processors10
+        //
+        //- if wanted is 2 then processor0,1 is enough
+        //- if wanted is not set then return highest valid range
+        //  (processors10 in above case)
+        //- if wanted cannot be matched (e.g. 37) return 0
+
+        // For marking off contiguous ranges
+        bitSet foundDirs;
+        if (wanted > 0)
+        {
+            foundDirs.resize(wanted);
+        }
+
         // Detect any processorsDDD or processorDDD
         label maxProc = -1;
         for (const fileName& dirN : dirNames)
@@ -1310,15 +1330,38 @@ Foam::label Foam::fileOperation::nProcs
                 splitProcessorPath(dirN, rp, rd, rl, group, rNum);
 
             maxProc = max(maxProc, readProci);
-            if (rNum != -1)
+
+            if (rNum > 0)       // processorsDDD where DDD>0
             {
-                // Direct detection of processorsDDD
-                maxProc = rNum-1;
-                break;
+                // Use processors number
+                maxProc = max(maxProc, rNum-1);
+                // Mark in cache. TBD separate handling for groups?
+                foundDirs.set(labelRange(0, rNum));
+
+                if (wanted == rNum)
+                {
+                    // Exact match of processorsDDD. Direct exit.
+                    maxProc = rNum-1;
+                    foundDirs.resize(rNum);
+                    break;
+                }
+            }
+            else if (readProci >= 0)
+            {
+                // Mark in cache
+                foundDirs.set(readProci);
             }
         }
         nProcs = maxProc+1;
 
+        // Override with any gaps in processorDDD numbering (can never happen
+        // with collated)
+        const label gapIndex = foundDirs.find_first_not();
+        if (gapIndex > 0)
+        {
+            nProcs = gapIndex-1;
+        }
+
         if (nProcs == 0 && Foam::isDir(dir/processorsBaseDir))
         {
             WarningInFunction
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
index 5de0a2a149..8053d6dfa8 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
@@ -862,7 +862,9 @@ public:
             virtual label nProcs
             (
                 const fileName& dir,
-                const fileName& local = ""
+                const fileName& local = "",
+                //! >0 if we know in advance what we're looking for
+                const label wantedNProcs = 0
             ) const;
 
             //- Get sorted list of times
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
index c505683363..182b526706 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
@@ -1983,7 +1983,7 @@ bool Foam::fileOperations::masterUncollatedFileOperation::readHeader
     {
         Pout<< "masterUncollatedFileOperation::readHeader :" << " ok:" << ok
             << " class:" << io.headerClassName()
-            << " for file:" << fName << endl;;
+            << " for file:" << fName << endl;
     }
     return ok;
 }
diff --git a/tutorials/mesh/parallel/cavity/Allrun b/tutorials/mesh/parallel/cavity/Allrun
index 75a0ebc376..49e9aa72a3 100755
--- a/tutorials/mesh/parallel/cavity/Allrun
+++ b/tutorials/mesh/parallel/cavity/Allrun
@@ -8,18 +8,19 @@ restore0Dir
 runApplication blockMesh
 
 decompDict5="-decomposeParDict system/decomposeParDict.5"
+fileHandler="-fileHandler uncollated"
 
 # redistributePar to do decomposition
-runParallel -s decompose redistributePar -decompose
+runParallel -s decompose redistributePar -decompose $fileHandler
 
 # Bit of renumbering and running
-runParallel -s CuthillMcKee renumberMesh -overwrite
-runParallel -s CuthillMcKee icoFoam
+runParallel -s CuthillMcKee renumberMesh -overwrite $fileHandler
+runParallel -s CuthillMcKee icoFoam $fileHandler
 
 # Bit of bad renumbering and running
 runParallel -s random renumberMesh \
-    -overwrite -dict system/renumberMeshDict-random
-runParallel -s random icoFoam
+    -overwrite -dict system/renumberMeshDict-random $fileHandler
+runParallel -s random icoFoam $fileHandler
 
 # Pick up last result
 cp system/controlDict-latestTime system/controlDict
@@ -27,13 +28,13 @@ cp system/controlDict-latestTime system/controlDict
 # Redistribute to 5 processors. Note that new processors only get written
 # a mesh to the current time (0.505). Use -overwrite instead to write the
 # mesh to constant.
-runParallel -s 5 $decompDict5 redistributePar -cellDist
+runParallel -s 5 $decompDict5 redistributePar -cellDist $fileHandler
 
 # Run a bit more
-runParallel -s 5 $decompDict5 icoFoam
+runParallel -s 5 $decompDict5 icoFoam $fileHandler
 
 # Reconstruct mesh and results. Note the time argument to make sure we
 # only pick up the new decomposition
-runParallel -s reconstruct -np 5 redistributePar -reconstruct -time 0.505:
+runParallel -s reconstruct -np 5 redistributePar -reconstruct -time 0.505: $fileHandler
 
 #------------------------------------------------------------------------------