diff --git a/lib/relation-definition.js b/lib/relation-definition.js
index b3dfe835..09849d12 100644
--- a/lib/relation-definition.js
+++ b/lib/relation-definition.js
@@ -203,14 +203,15 @@ util.inherits(HasOne, Relation);
  * @param {*} foreignKey The foreign key
  * @returns {Object} The relation object
  */
-function findBelongsTo(model, foreignKey) {
-  var relations = model.relations;
+function findBelongsTo(modelFrom, modelTo, keyTo) {
+  var relations = modelFrom.relations;
   var keys = Object.keys(relations);
   for (var k = 0; k < keys.length; k++) {
     var rel = relations[keys[k]];
     if (rel.type === RelationTypes.belongsTo &&
-      rel.keyFrom === foreignKey) {
-      return keys[k];
+      rel.modelTo === modelTo &&
+      rel.keyTo === keyTo) {
+      return rel.keyFrom;
     }
   }
   return null;
@@ -378,25 +379,30 @@ HasMany.prototype.destroyById = function (id, cb) {
 // Create an instance of the target model and connect it to the instance of
 // the source model by creating an instance of the through model
 HasManyThrough.prototype.create = function create(data, done) {
-  var modelTo = this.definition.modelTo;
-  var modelThrough = this.definition.modelThrough;
-  var fk = this.definition.keyTo;
-  var fk2 = this.definition.keyThrough;
+  var definition = this.definition;
+  var modelTo = definition.modelTo;
+  var modelThrough = definition.modelThrough;
 
   if (typeof data === 'function' && !done) {
     done = data;
     data = {};
   }
 
-  var self = this.modelInstance;
+  var modelInstance = this.modelInstance;
+
   // First create the target model
   modelTo.create(data, function (err, ac) {
     if (err) {
       return done && done(err, ac);
     }
+    // The primary key for the target model
+    var pk2 = modelTo.dataSource.idName(modelTo.modelName) || 'id';
+    var fk1 = findBelongsTo(modelThrough, definition.modelFrom,
+      definition.keyFrom);
+    var fk2 = findBelongsTo(modelThrough, definition.modelTo, pk2);
     var d = {};
-    d[findBelongsTo(modelThrough, fk)] = self;
-    d[findBelongsTo(modelThrough, fk2)] = ac;
+    d[fk1] = modelInstance[definition.keyFrom];
+    d[fk2] = ac[pk2];
     // Then create the through model
     modelThrough.create(d, function (e) {
       if (e) {
@@ -416,17 +422,28 @@ HasManyThrough.prototype.create = function create(data, done) {
  * @param {Object|ID} acInst The actual instance or id value
  */
 HasManyThrough.prototype.add = function (acInst, done) {
-  var modelThrough = this.definition.modelThrough;
-  var fk = this.definition.keyTo;
-  var fk2 = this.definition.keyThrough;
-  var pk = this.definition.keyFrom;
+  var definition = this.definition;
+  var modelThrough = definition.modelThrough;
+  var modelTo = definition.modelTo;
+  var pk1 = definition.keyFrom;
 
   var data = {};
   var query = {};
-  query[fk] = this[pk];
-  data[findBelongsTo(modelThrough, fk)] = this.modelInstance;
-  query[fk2] = acInst[pk] || acInst;
-  data[findBelongsTo(modelThrough, fk2)] = acInst;
+
+  var fk1 = findBelongsTo(modelThrough, definition.modelFrom,
+    definition.keyFrom);
+
+  // The primary key for the target model
+  var pk2 = modelTo.dataSource.idName(modelTo.modelName) || 'id';
+
+  var fk2 = findBelongsTo(modelThrough, definition.modelTo, pk2);
+
+  query[fk1] = this.modelInstance[pk1];
+  query[fk2] = acInst[pk2] || acInst;
+
+  data[fk1] = this.modelInstance[pk1];
+  data[fk2] = acInst[pk2] || acInst;
+
   // Create an instance of the through model
   modelThrough.findOrCreate({where: query}, data, done);
 };