diff --git a/lib-es5/utils/index.js b/lib-es5/utils/index.js
index 7bce0170..defd847c 100644
--- a/lib-es5/utils/index.js
+++ b/lib-es5/utils/index.js
@@ -81,7 +81,7 @@ module.exports = {
   },
   ensurePresenceOf
 };
-exports = module.exports;
+let exports = module.exports;
 var utils = module.exports;
 
 try {
@@ -239,9 +239,19 @@ function process_custom_function(customFunction) {
   }
   if (customFunction.function_type === "remote") {
     return [customFunction.function_type, base64EncodeURL(customFunction.source)].join(":");
-  } else {
-    return [customFunction.function_type, customFunction.source].join(":");
   }
+  return [customFunction.function_type, customFunction.source].join(":");
+}
+
+/**
+ * Parse custom_pre_function options
+ * @private
+ * @param {object|*} customPreFunction a custom function object containing function_type and source values
+ * @return {string|*} custom_pre_function transformation string
+ */
+function process_custom_pre_function(customPreFunction) {
+  var result = process_custom_function(customPreFunction);
+  return utils.isString(result) ? `pre:${result}` : null;
 }
 
 /**
@@ -565,6 +575,7 @@ function generate_transformation_string(options) {
   var underlay = process_layer(utils.option_consume(options, "underlay"));
   var ifValue = process_if(utils.option_consume(options, "if"));
   var custom_function = process_custom_function(utils.option_consume(options, "custom_function"));
+  var custom_pre_function = process_custom_pre_function(utils.option_consume(options, "custom_pre_function"));
   var fps = utils.option_consume(options, 'fps');
   if (isArray(fps)) {
     fps = fps.join('-');
@@ -579,7 +590,7 @@ function generate_transformation_string(options) {
     dpr: normalize_expression(dpr),
     e: normalize_expression(effect),
     fl: flags,
-    fn: custom_function,
+    fn: custom_function || custom_pre_function,
     fps: fps,
     h: normalize_expression(height),
     ki: normalize_expression(utils.option_consume(options, "keyframe_interval")),
@@ -1546,4 +1557,4 @@ exports.build_streaming_profiles_param = build_streaming_profiles_param;
 exports.hashToParameters = hashToParameters;
 exports.present = present;
 exports.only = only;
-exports.jsonArrayParam = jsonArrayParam;
\ No newline at end of file
+exports.jsonArrayParam = jsonArrayParam;
diff --git a/lib/utils/index.js b/lib/utils/index.js
index 20f315c6..505bd3d3 100644
--- a/lib/utils/index.js
+++ b/lib/utils/index.js
@@ -213,9 +213,19 @@ function process_custom_function(customFunction) {
   }
   if (customFunction.function_type === "remote") {
     return [customFunction.function_type, base64EncodeURL(customFunction.source)].join(":");
-  } else {
-    return [customFunction.function_type, customFunction.source].join(":");
   }
+  return [customFunction.function_type, customFunction.source].join(":");
+}
+
+/**
+ * Parse custom_pre_function options
+ * @private
+ * @param {object|*} customPreFunction a custom function object containing function_type and source values
+ * @return {string|*} custom_pre_function transformation string
+ */
+function process_custom_pre_function(customPreFunction) {
+  let result = process_custom_function(customPreFunction);
+  return utils.isString(result) ? `pre:${result}` : null;
 }
 
 /**
@@ -543,6 +553,7 @@ function generate_transformation_string(options) {
   let underlay = process_layer(utils.option_consume(options, "underlay"));
   let ifValue = process_if(utils.option_consume(options, "if"));
   let custom_function = process_custom_function(utils.option_consume(options, "custom_function"));
+  let custom_pre_function = process_custom_pre_function(utils.option_consume(options, "custom_pre_function"));
   let fps = utils.option_consume(options, 'fps');
   if (isArray(fps)) {
     fps = fps.join('-');
@@ -557,7 +568,7 @@ function generate_transformation_string(options) {
     dpr: normalize_expression(dpr),
     e: normalize_expression(effect),
     fl: flags,
-    fn: custom_function,
+    fn: custom_function || custom_pre_function,
     fps: fps,
     h: normalize_expression(height),
     ki: normalize_expression(utils.option_consume(options, "keyframe_interval")),
diff --git a/test/cloudinary_spec.js b/test/cloudinary_spec.js
index 2d1a7c42..8d6f0937 100644
--- a/test/cloudinary_spec.js
+++ b/test/cloudinary_spec.js
@@ -424,7 +424,7 @@ describe("cloudinary", function () {
   it('should support custom function of type wasm with a source', function () {
     var options, result;
     options = {
-      custom_function: {function_type: 'wasm', source: 'blur.wasm'}
+      custom_function: { function_type: 'wasm', source: 'blur.wasm' },
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
@@ -433,7 +433,7 @@ describe("cloudinary", function () {
   it('should support arbitrary custom function types', function () {
     var options, result;
     options = {
-      custom_function: {function_type: 'amazing', source: 'awesome'}
+      custom_function: { function_type: 'amazing', source: 'awesome' },
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
@@ -442,7 +442,7 @@ describe("cloudinary", function () {
   it('should support custom function with no source', function () {
     var options, result;
     options = {
-      custom_function: {function_type: 'wasm'}
+      custom_function: { function_type: 'wasm' },
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
@@ -451,7 +451,7 @@ describe("cloudinary", function () {
   it('should support custom function with no function_type', function () {
     var options, result;
     options = {
-      custom_function:  {source: 'blur.wasm'}
+      custom_function: { source: 'blur.wasm' },
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
@@ -460,7 +460,7 @@ describe("cloudinary", function () {
   it('should support custom function that is not an object', function () {
     var options, result;
     options = {
-      custom_function: []
+      custom_function: [],
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
@@ -469,30 +469,56 @@ describe("cloudinary", function () {
   it('should support custom function with no function_type or source', function () {
     var options, result;
     options = {
-      custom_function: {}
+      custom_function: {},
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
     expect(result).to.eql("http://res.cloudinary.com/test123/image/upload/fn_:/test");
   });
-  it('should support custom function of type remote', function() {
+  it('should support custom function of type remote', function () {
     var options, result;
     options = {
-      custom_function: {function_type: 'remote', source: 'https://df34ra4a.execute-api.us-west-2.amazonaws.com/default/cloudinaryFunction'}
+      custom_function: {
+        function_type: 'remote',
+        source:
+          'https://df34ra4a.execute-api.us-west-2.amazonaws.com/default/cloudinaryFunction',
+      },
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
     expect(result).to.eql("http://res.cloudinary.com/test123/image/upload/fn_remote:aHR0cHM6Ly9kZjM0cmE0YS5leGVjdXRlLWFwaS51cy13ZXN0LTIuYW1hem9uYXdzLmNvbS9kZWZhdWx0L2Nsb3VkaW5hcnlGdW5jdGlvbg==/test");
   });
-  it('should should not include custom function with undefined value', function() {
+  it('should should not include custom function with undefined value', function () {
     var options, result;
     options = {
-      custom_function: undefined
+      custom_function: undefined,
     };
     result = cloudinary.utils.url("test", options);
     expect(options).to.eql({});
     expect(result).to.eql("http://res.cloudinary.com/test123/image/upload/test");
   });
+  it('should support custom pre function', function () {
+    var options, result;
+    options = {
+      custom_pre_function: {
+        function_type: 'remote',
+        source:
+          'https://df34ra4a.execute-api.us-west-2.amazonaws.com/default/cloudinaryFunction',
+      },
+    };
+    result = cloudinary.utils.url("test", options);
+    expect(options).to.eql({});
+    expect(result).to.eql("http://res.cloudinary.com/test123/image/upload/fn_pre:remote:aHR0cHM6Ly9kZjM0cmE0YS5leGVjdXRlLWFwaS51cy13ZXN0LTIuYW1hem9uYXdzLmNvbS9kZWZhdWx0L2Nsb3VkaW5hcnlGdW5jdGlvbg==/test");
+  });
+  it('should support custom pre function with no function_type or source', function () {
+    var options, result;
+    options = {
+      custom_pre_function: {},
+    };
+    result = cloudinary.utils.url("test", options);
+    expect(options).to.eql({});
+    expect(result).to.eql("http://res.cloudinary.com/test123/image/upload/fn_pre::/test");
+  });
   it("should support density", function () {
     var options, result;
     options = {