diff --git a/js/server/modules/@arangodb/cluster.js b/js/server/modules/@arangodb/cluster.js
index b94760a837..58f2f5d39f 100644
--- a/js/server/modules/@arangodb/cluster.js
+++ b/js/server/modules/@arangodb/cluster.js
@@ -861,6 +861,86 @@ function cleanupCurrentCollections (plannedCollections, currentCollections,
 /// replicated shards)
 ////////////////////////////////////////////////////////////////////////////////
 
+function synchronizeOneShard(database, shard, planId, leader) {
+  // synchronize this shard from the leader
+  // this function will throw if anything goes wrong
+
+  const rep = require("@arangodb/replication");
+
+  console.info("trying to synchronize local shard '%s/%s' for central '%s/%s'",
+               database,
+               shard,
+               database,
+               planId);
+  try {
+    var ep = ArangoClusterInfo.getServerEndpoint(leader);
+    // First once without a read transaction:
+    var sy = rep.syncCollection(shard, 
+        { endpoint: ep, incremental: true,
+          keepBarrier: true });
+    if (sy.error) {
+      console.error("Could not initially synchronize shard ", shard, sy);
+      throw "Initial sync failed";
+    } else {
+      if (sy.collections.length === 0 ||
+          sy.collections[0].name !== shard) {
+        cancelBarrier(ep, database, sy.barrierId);
+        throw "Shard seems to be gone from leader!";
+      } else {
+        var ok = false;
+        // Now start a read transaction to stop writes:
+        var lockJobId = false;
+        try {
+          lockJobId = startReadLockOnLeader(ep, database,
+                                            shard, 300);
+          console.debug("lockJobId:", lockJobId);
+        }
+        catch (err1) {
+          console.error("Exception in startReadLockOnLeader:", err1);
+        }
+        finally {
+          cancelBarrier(ep, database, sy.barrierId);
+        }
+        if (lockJobId !== false) {
+          try {
+            var sy2 = rep.syncCollectionFinalize(
+              database, shard, sy.collections[0].id, 
+              sy.lastLogTick, { endpoint: ep });
+            if (sy2.error) {
+              console.error("Could not synchronize shard", shard,
+                            sy2);
+              ok = false;
+            } else {
+              ok = addShardFollower(ep, database, shard);
+            }
+          }
+          catch (err3) {
+            console.error("Exception in syncCollectionFinalize:", err3);
+          }
+          finally {
+            if (!cancelReadLockOnLeader(ep, database, 
+                                        lockJobId)) {
+              console.error("Read lock has timed out for shard", shard);
+              ok = false;
+            }
+          }
+        } else {
+          console.error("lockJobId was false");
+        }
+        if (ok) {
+          console.info("Synchronization worked for shard", shard);
+        } else {
+          throw "Did not work.";  // just to log below in catch
+        }
+      }
+    }
+  }
+  catch (err2) {
+    console.error("synchronization of local shard '%s/%s' for central '%s/%s' failed: %s",
+                  database, shard, database, planId, JSON.stringify(err2));
+  }
+}
+
 function synchronizeLocalFollowerCollections (plannedCollections,
                                               currentCollections) {
   var ourselves = global.ArangoServerState.id();
@@ -870,8 +950,6 @@ function synchronizeLocalFollowerCollections (plannedCollections,
   var localDatabases = getLocalDatabases();
   var database;
 
-  var rep = require("@arangodb/replication");
-
   // iterate over all matching databases
   for (database in plannedCollections) {
     if (plannedCollections.hasOwnProperty(database)) {
@@ -911,84 +989,8 @@ function synchronizeLocalFollowerCollections (plannedCollections,
                                     "come back later to this shard...");
                     } else {
                       if (inCurrent.servers.indexOf(ourselves) === -1) {
-                        // we not in there - must synchronize this shard from
-                        // the leader
-                        console.info("trying to synchronize local shard '%s/%s' for central '%s/%s'",
-                                     database,
-                                     shard,
-                                     database,
-                                     collInfo.planId);
-                        try {
-                          var ep = ArangoClusterInfo.getServerEndpoint(
-                                inCurrent.servers[0]);
-                          // First once without a read transaction:
-                          var sy = rep.syncCollection(shard, 
-                            { endpoint: ep, incremental: true,
-                              keepBarrier: true });
-                          if (sy.error) {
-                            console.error("Could not initially synchronize shard ", shard, sy);
-                          } else {
-                            if (sy.collections.length == 0 ||
-                                sy.collections[0].name != shard) {
-                              cancelBarrier(ep, database, sy.barrierId);
-                              throw "Shard seems to be gone from leader!";
-                            } else {
-                              var ok = false;
-                              // Now start a read transaction to stop writes:
-                              var lockJobId = false;
-                              try {
-                                lockJobId = startReadLockOnLeader(ep, database,
-                                                                  shard, 300);
-                                console.debug("lockJobId:", lockJobId);
-                              }
-                              catch (err1) {
-                                console.error("Exception in startReadLockOnLeader:", err1);
-                              }
-                              finally {
-                                cancelBarrier(ep, database, sy.barrierId);
-                              }
-                              if (lockJobId !== false) {
-                                try {
-                                  var sy2 = rep.syncCollectionFinalize(
-                                    database, shard, sy.collections[0].id, 
-                                    sy.lastLogTick, { endpoint: ep });
-                                  if (sy2.error) {
-                                    console.error("Could not synchronize shard", shard,
-                                                  sy2);
-                                    ok = false;
-                                  } else {
-                                    ok = addShardFollower(ep, database, shard);
-                                  }
-                                }
-                                catch (err3) {
-                                  console.error("Exception in syncCollectionFinalize:", err3);
-                                }
-                                finally {
-                                  if (!cancelReadLockOnLeader(ep, database, 
-                                                              lockJobId)) {
-                                    console.error("Read lock has timed out for shard", shard);
-                                    ok = false;
-                                  }
-                                }
-                              } else {
-                                console.error("lockJobId was false");
-                              }
-                              if (ok) {
-                                console.info("Synchronization worked for shard", shard);
-                              } else {
-                                throw "Did not work.";  // just to log below in catch
-                              }
-                            }
-                          }
-                        }
-                        catch (err2) {
-                          console.error("synchronization of local shard '%s/%s' for central '%s/%s' failed: %s",
-                                        database,
-                                        shard,
-                                        database,
-                                        collInfo.planId,
-                                        JSON.stringify(err2));
-                        }
+                        synchronizeOneShard(database, shard, collInfo.planId,
+                                            inCurrent.servers[0]);
                       }
                     }
                   }