diff --git a/lib/repository.js b/lib/repository.js
index 22f10668f..f311900eb 100644
--- a/lib/repository.js
+++ b/lib/repository.js
@@ -1686,6 +1686,7 @@ Repository.prototype.refreshIndex = function(callback) {
  * @param {Signature}         signature
  * @param {Merge.PREFERENCE}  mergePreference
  * @param {MergeOptions}      mergeOptions
+ * @param {MergeBranchOptions} mergeBranchOptions
  * @return {Oid|Index}  A commit id for a succesful merge or an index for a
  *                      merge with conflicts
  */
@@ -1695,13 +1696,23 @@ Repository.prototype.mergeBranches = function(
   signature,
   mergePreference,
   mergeOptions,
-  processMergeMessageCallback
+  mergeBranchOptions
 ) {
   const repo = this;
   let fromBranch;
   let toBranch;
-  processMergeMessageCallback = processMergeMessageCallback ||
+  // Support old parameter `processMergeMessageCallback`
+  const isOldOptionParameter = typeof mergeBranchOptions === "function";
+  if (isOldOptionParameter) {
+    console.error("DeprecationWarning: Repository#mergeBranches parameter " +
+                  "processMergeMessageCallback, use MergeBranchOptions");
+  }
+  const processMergeMessageCallback = mergeBranchOptions &&
+    (isOldOptionParameter ?
+      mergeBranchOptions :
+      mergeBranchOptions.processMergeMessageCallback) ||
     function (message) { return message; };
+  const signingCallback = mergeBranchOptions && mergeBranchOptions.signingCb;
 
   mergePreference = mergePreference || NodeGit.Merge.PREFERENCE.NONE;
   mergeOptions = normalizeOptions(mergeOptions, NodeGit.MergeOptions);
@@ -1819,6 +1830,17 @@ Repository.prototype.mergeBranches = function(
           return Promise.all([oid, processMergeMessageCallback(message)]);
         })
         .then(([oid, message]) => {
+          if (signingCallback) {
+            return repo.createCommitWithSignature(
+              toBranch.name(),
+              signature,
+              signature,
+              message,
+              oid,
+              [toCommitOid, fromCommitOid],
+              signingCallback
+            );
+          }
           return repo.createCommit(
             toBranch.name(),
             signature,
diff --git a/test/tests/merge.js b/test/tests/merge.js
index 80bb0589d..00387da82 100644
--- a/test/tests/merge.js
+++ b/test/tests/merge.js
@@ -646,9 +646,11 @@ describe("Merge", function() {
           ourSignature,
           NodeGit.Merge.PREFERENCE.NO_FASTFORWARD,
           null,
-          function(message) {
-            assert(message === "Merge branch 'theirs' into ours");
-            return "We manipulated the message, HAH.";
+          {
+            processMergeMessageCallback: function(message) {
+              assert(message === "Merge branch 'theirs' into ours");
+              return "We manipulated the message, HAH.";
+            }
           }
         );
       })
@@ -803,9 +805,11 @@ describe("Merge", function() {
           ourSignature,
           NodeGit.Merge.PREFERENCE.NO_FASTFORWARD,
           null,
-          function(message) {
-            assert(message === "Merge branch 'theirs' into ours");
-            return Promise.resolve("We manipulated the message, HAH.");
+          {
+            processMergeMessageCallback: function(message) {
+              assert(message === "Merge branch 'theirs' into ours");
+              return Promise.resolve("We manipulated the message, HAH.");
+            }
           }
         );
       })