diff --git a/src/libCom/ellLib/ellLib.h b/src/libCom/ellLib/ellLib.h
index f99859f3d..300a2df3f 100644
--- a/src/libCom/ellLib/ellLib.h
+++ b/src/libCom/ellLib/ellLib.h
@@ -56,6 +56,8 @@ epicsShareFunc void ellInsert (ELLLIST *plist, ELLNODE *pPrev, ELLNODE *pNode);
 epicsShareFunc ELLNODE * ellNth (ELLLIST *pList, int nodeNum);
 epicsShareFunc ELLNODE * ellNStep (ELLNODE *pNode, int nStep);
 epicsShareFunc int  ellFind (ELLLIST *pList, ELLNODE *pNode);
+typedef int (*pListCmp)(ELLNODE* A, ELLNODE* B);
+epicsShareFunc void ellSortStable(ELLLIST *pList, pListCmp);
 epicsShareFunc void ellFree2 (ELLLIST *pList, FREEFUNC freeFunc);
 epicsShareFunc void ellVerify (ELLLIST *pList);
 
diff --git a/src/libCom/ellLib/ellSort.c b/src/libCom/ellLib/ellSort.c
new file mode 100644
index 000000000..89f3f3819
--- /dev/null
+++ b/src/libCom/ellLib/ellSort.c
@@ -0,0 +1,80 @@
+/*
+ * Use of mergesort algorithm based on analysis by
+ * http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
+ */
+#include <stdlib.h>
+
+#define epicsExportSharedSymbols
+#include "epicsAssert.h"
+#include "ellLib.h"
+
+static void ellMoveN(ELLLIST* pTo, ELLLIST* pFrom, int count )
+{
+    for(;count && ellCount(pFrom); count--) {
+        ELLNODE *node = ellGet(pFrom);
+        ellAdd(pTo, node);
+    }
+}
+
+/* Stable (MergeSort) to given list.
+ * The comparison function cmp(A,B) is expected
+ * to return -1 for A<B, 0 for A==B, and 1 for A>B.
+ */
+void ellSortStable(ELLLIST *pList, pListCmp cmp)
+{
+    ELLLIST INP, P, Q;
+    size_t insize = 1; /* initial sub-list size */
+    if(ellCount(pList)<=1)
+        return;
+
+    ellInit(&INP);
+    ellInit(&P);
+    ellInit(&Q);
+
+    /* Process is to iteratively sort
+     * a sequence of sub-lists of size 'insize'
+     */
+
+    while(insize < ellCount(pList)) {
+
+        assert(ellCount(&INP)==0);
+
+        /* shift previous results to inputs */
+        ellConcat(&INP, pList);
+        
+        assert(ellCount(pList)==0);
+
+        while(ellCount(&INP))
+        {
+            ELLNODE *p, *q;
+
+            assert(ellCount(&P)==0);
+            assert(ellCount(&Q)==0);
+
+            /* Pull out the next pair of sub-lists */
+            ellMoveN(&Q, &INP, insize);
+            ellMoveN(&P, &INP, insize);
+
+            /* merge these sub-lists */
+            while((p=ellFirst(&P)) && (q=ellFirst(&Q)))
+            {
+                if((*cmp)(p,q) < 0) {
+                    ellAdd(pList, ellGet(&P));
+                } else {
+                    ellAdd(pList, ellGet(&Q));
+                }
+            }
+
+            /* concatinate any remaining to result */
+            if(ellFirst(&P))
+                ellConcat(pList, &P);
+            else if(ellFirst(&Q))
+                ellConcat(pList, &Q);
+
+            assert(!ellFirst(&P) && !ellFirst(&Q));
+        }
+
+        insize *= 2;
+    }
+
+}