diff --git a/thorlcr/activities/nsplitter/thnsplitterslave.cpp b/thorlcr/activities/nsplitter/thnsplitterslave.cpp
index de5e5db6c54..af9eb9469fa 100644
--- a/thorlcr/activities/nsplitter/thnsplitterslave.cpp
+++ b/thorlcr/activities/nsplitter/thnsplitterslave.cpp
@@ -405,7 +405,7 @@ class NSplitterSlaveActivity : public CSlaveActivity, implements ISharedSmartBuf
     {
         PARENT::gatherActiveStats(activeStats);
         if (sharedRowStream)
-            sharedRowStream->mergeStats(activeStats);
+            ::mergeStats(activeStats, sharedRowStream);
     }
 // ISharedSmartBufferCallback impl.
     virtual void paged() { pagedOut = true; }
diff --git a/thorlcr/thorutil/thbuf.cpp b/thorlcr/thorutil/thbuf.cpp
index 9c0e6dcfa4d..b3e66536a21 100644
--- a/thorlcr/thorutil/thbuf.cpp
+++ b/thorlcr/thorutil/thbuf.cpp
@@ -1175,8 +1175,9 @@ class CSharedWriteAheadBase : public CSimpleInterface, implements ISharedSmartBu
             queryCOutput(c).reset();
         inMemRows->reset(0);
     }
-    virtual void mergeStats(CRuntimeStatisticCollection & target) const override
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const override
     {
+        return 0;
     }
 friend class COutput;
 friend class CRowSet;
@@ -1570,19 +1571,25 @@ class CSharedWriteAheadDisk : public CSharedWriteAheadBase
         tempFileIO->setSize(0);
         tempFileOwner->noteSize(0);
     }
-    virtual void mergeStats(CRuntimeStatisticCollection & target) const override
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const override
     {
-        ::mergeStats(target, tempFileIO);
-        unsigned __int64 diskWriteSize = target.queryStatistic(StSizeDiskWrite).getClear();
-        if (diskWriteSize)
-            target.setStatistic(StSizeSpillFile, diskWriteSize);
-        unsigned __int64 ioTime = target.queryStatistic(StCycleDiskWriteIOCycles).getClear();
-        if (ioTime)
+        switch (kind)
         {
-            target.queryStatistic(StTimeDiskWriteIO).getClear();
-            target.setStatistic(StTimeSpillElapsed, ioTime);
+            case StSizeSpillFile:
+                return tempFileIO->getStatistic(StSizeDiskWrite);
+                break;
+            case StCycleDiskWriteIOCycles:
+            case StTimeDiskWriteIO:
+            case StSizeDiskWrite:
+                return 0;
+            case StNumSpills:
+                return 1;
+            case StTimeSpillElapsed:
+                return tempFileIO->getStatistic(StCycleDiskWriteIOCycles);
+                break;
+            default:
+                return tempFileIO->getStatistic(kind);
         }
-        target.setStatistic(StNumSpills, 1);
     }
 };
 
@@ -2171,21 +2178,31 @@ class CSharedFullSpillingWriteAhead : public CInterfaceOf<ISharedRowStreamReader
         nextInputReadEog = false;
         endOfInput = false;
     }
-    virtual void mergeStats(CRuntimeStatisticCollection & target) const override
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const override
     {
-        if (iFileIO)
-            ::mergeStats(target, iFileIO);
-        target.merge(inactiveStats);
-        unsigned __int64 diskWriteSize = target.queryStatistic(StSizeDiskWrite).getClear();
-        if (diskWriteSize)
-            target.setStatistic(StSizeSpillFile, diskWriteSize);
-        unsigned __int64 ioTime = target.queryStatistic(StCycleDiskWriteIOCycles).getClear();
-        if (ioTime)
+        StatisticKind useKind;
+        switch (kind)
         {
-            target.queryStatistic(StTimeDiskWriteIO).getClear();
-            target.setStatistic(StTimeSpillElapsed, ioTime);
-        }
-        target.setStatistic(StNumSpills, 1);
+            case StSizeSpillFile:
+                useKind = StSizeDiskWrite;
+                break;
+            case StCycleDiskWriteIOCycles:
+            case StTimeDiskWriteIO:
+            case StSizeDiskWrite:
+                return 0;
+            case StNumSpills:
+                return 1;
+            case StTimeSpillElapsed:
+                useKind = StCycleDiskWriteIOCycles;
+                break;
+            default:
+                useKind = kind;
+        }
+        unsigned __int64 v = 0;
+        if (likely(iFileIO))
+            v = iFileIO->getStatistic(useKind);
+        v += inactiveStats.getStatisticValue(useKind);
+        return v;
     }
 };
 
diff --git a/thorlcr/thorutil/thbuf.hpp b/thorlcr/thorutil/thbuf.hpp
index 58f73784ee6..4bae5294652 100644
--- a/thorlcr/thorutil/thbuf.hpp
+++ b/thorlcr/thorutil/thbuf.hpp
@@ -70,7 +70,7 @@ interface ISharedRowStreamReader : extends IInterface
     virtual IRowStream *queryOutput(unsigned output) = 0;
     virtual void cancel()=0;
     virtual void reset() = 0;
-    virtual void mergeStats(CRuntimeStatisticCollection & target) const = 0;
+    virtual unsigned __int64 getStatistic(StatisticKind kind) const = 0;
 };