diff --git a/lib/fp/baseConvert.js b/lib/fp/baseConvert.js
index 5d9c305c8..ee3f7c697 100644
--- a/lib/fp/baseConvert.js
+++ b/lib/fp/baseConvert.js
@@ -40,21 +40,16 @@ function baseConvert(util, name, func) {
       keys = _.keys,
       rearg = _.rearg;
 
-  var baseAry = function(func, n) {
-    return function() {
-      var args = arguments,
-          length = Math.min(args.length, n);
+  var baseArity = function(func, n) {
+    return n == 2
+      ? function(a, b) { return func.apply(undefined, arguments); }
+      : function(a) { return func.apply(undefined, arguments); };
+  };
 
-      switch (length) {
-        case 1: return func(args[0]);
-        case 2: return func(args[0], args[1]);
-      }
-      args = Array(length);
-      while (length--) {
-        args[length] = arguments[length];
-      }
-      return func.apply(undefined, args);
-    };
+  var baseAry = function(func, n) {
+    return n == 2
+      ? function(a, b) { return func(a, b); }
+      : function(a) { return func(a); };
   };
 
   var cloneArray = function(array) {
@@ -83,6 +78,13 @@ function baseConvert(util, name, func) {
     });
   };
 
+  var iterateeRearg = function(func, indexes) {
+    return overArg(func, function(func) {
+      var n = indexes.length;
+      return baseArity(rearg(baseAry(func, n), indexes), n);
+    });
+  };
+
   var overArg = function(func, iteratee, retArg) {
     return function() {
       var length = arguments.length,
@@ -172,6 +174,10 @@ function baseConvert(util, name, func) {
           if (n) {
             result = iterateeAry(result, n);
           }
+          var indexes = mapping.iterateeRearg[name];
+          if (indexes) {
+            result = iterateeRearg(result, indexes);
+          }
           if (cap > 1) {
             result = curry(result, cap);
           }
diff --git a/lib/fp/mapping.js b/lib/fp/mapping.js
index 898188527..4f1e607ee 100644
--- a/lib/fp/mapping.js
+++ b/lib/fp/mapping.js
@@ -102,23 +102,30 @@ module.exports = {
     3:[
         'assignInWith', 'assignWith', 'clamp', 'differenceBy', 'differenceWith',
         'getOr', 'inRange', 'intersectionBy', 'intersectionWith', 'isEqualWith',
-        'isMatchWith', 'mergeWith', 'pullAllBy', 'reduce',
-        'reduceRight', 'replace', 'set', 'slice', 'sortedIndexBy', 'sortedLastIndexBy',
-        'transform', 'unionBy', 'unionWith', 'xorBy', 'xorWith', 'zipWith'
+        'isMatchWith', 'mergeWith', 'pullAllBy', 'reduce', 'reduceRight', 'replace',
+        'set', 'slice', 'sortedIndexBy', 'sortedLastIndexBy', 'transform', 'unionBy',
+        'unionWith', 'xorBy', 'xorWith', 'zipWith'
       ],
     4:[
         'fill', 'setWith'
       ]
   },
 
-  /** Used to map ary to rearg configs by method ary. */
+  /** Used to map ary to rearg configs. */
   'aryRearg': {
     2: [1, 0],
     3: [2, 1, 0],
     4: [3, 2, 0, 1]
   },
 
-  /** Used to map ary to rearg configs by method names. */
+  /** Used to map method names to iteratee rearg configs. */
+  'iterateeRearg': {
+    'findKey': [1],
+    'findLastKey': [1],
+    'mapKeys': [1]
+  },
+
+  /** Used to map method names to rearg configs. */
   'methodRearg': {
     'clamp': [2, 0, 1],
     'reduce': [2, 0, 1],
diff --git a/test/test-fp.js b/test/test-fp.js
index 0f9821c97..41ff5d0b8 100644
--- a/test/test-fp.js
+++ b/test/test-fp.js
@@ -773,6 +773,26 @@
 
   /*--------------------------------------------------------------------------*/
 
+  QUnit.module('key methods');
+
+  (function() {
+    var object = { 'a': 1 };
+
+    QUnit.test('should provide the correct `iteratee` arguments', function(assert) {
+      assert.expect(1);
+
+      var args;
+
+      var actual = fp.findKey(function() {
+        args || (args = _.map(arguments, _.cloneDeep));
+      }, object);
+
+      assert.deepEqual(args, ['a'], 'fp.findKey');
+    });
+  }());
+
+  /*--------------------------------------------------------------------------*/
+
   QUnit.module('mutation methods');
 
   (function() {
@@ -909,18 +929,16 @@
       var args,
           value = _.clone(object);
 
-      var actual = fp.assignWith(function(objValue, srcValue) {
+      var actual = fp.assignWith(function() {
         args || (args = _.map(arguments, _.cloneDeep));
-        return srcValue;
       }, { 'b': 2 }, value);
 
       assert.deepEqual(args, [undefined, 2, 'b', { 'a': 1 }, { 'b': 2 }], 'fp.assignWith');
 
       args = undefined;
       value = _.clone(object);
-      actual = fp.extendWith(function(objValue, srcValue) {
+      actual = fp.extendWith(function() {
         args || (args = _.map(arguments, _.cloneDeep));
-        return srcValue;
       }, { 'b': 2 }, value);
 
       assert.deepEqual(args, [undefined, 2, 'b', { 'a': 1 }, { 'b': 2 }], 'fp.extendWith');
@@ -930,11 +948,8 @@
 
       args = undefined;
       value = { 'a': [1] };
-      actual = fp.mergeWith(function(objValue, srcValue) {
+      actual = fp.mergeWith(function() {
         args || (args = _.map(arguments, _.cloneDeep));
-        if (_.isArray(objValue)) {
-          return objValue.concat(srcValue);
-        }
       }, { 'a': [2, 3] }, value);
 
       args[5] = _.omitBy(args[5], _.isFunction);