diff --git a/lib-es5/utils/index.js b/lib-es5/utils/index.js
index 7d9b72d1..edbdb4c9 100644
--- a/lib-es5/utils/index.js
+++ b/lib-es5/utils/index.js
@@ -156,9 +156,10 @@ function normalize_expression(expression) {
   });
 
   var predefinedVarsPattern = "(" + Object.keys(PREDEFINED_VARS).join("|") + ")";
-  var predefinedVarsReplaceRE = new RegExp(predefinedVarsPattern, "g");
-  expression = expression.replace(predefinedVarsReplaceRE, function (match, p1, offset) {
-    return expression[offset - 1] === '$' ? match : PREDEFINED_VARS[match];
+  var userVariablePattern = '(\\$_*[^_ ]+)';
+  var variablesReplaceRE = new RegExp(`${userVariablePattern}|${predefinedVarsPattern}`, "g");
+  expression = expression.replace(variablesReplaceRE, function (match) {
+    return PREDEFINED_VARS[match] || match;
   });
 
   return expression.replace(/[ _]+/g, '_');
diff --git a/lib/utils/index.js b/lib/utils/index.js
index 13867857..3170346d 100644
--- a/lib/utils/index.js
+++ b/lib/utils/index.js
@@ -141,8 +141,9 @@ function normalize_expression(expression) {
   expression = expression.replace(operatorsReplaceRE, match => CONDITIONAL_OPERATORS[match]);
 
   const predefinedVarsPattern = "(" + Object.keys(PREDEFINED_VARS).join("|") + ")";
-  const predefinedVarsReplaceRE = new RegExp(predefinedVarsPattern, "g");
-  expression = expression.replace(predefinedVarsReplaceRE, (match, p1, offset) => (expression[offset - 1] === '$' ? match : PREDEFINED_VARS[match]));
+  const userVariablePattern = '(\\$_*[^_ ]+)';
+  const variablesReplaceRE = new RegExp(`${userVariablePattern}|${predefinedVarsPattern}`, "g");
+  expression = expression.replace(variablesReplaceRE, (match) => (PREDEFINED_VARS[match] || match));
 
   return expression.replace(/[ _]+/g, '_');
 }
diff --git a/test/unit/cloudinary_spec.js b/test/unit/cloudinary_spec.js
index 27ed5703..f44bb58a 100644
--- a/test/unit/cloudinary_spec.js
+++ b/test/unit/cloudinary_spec.js
@@ -795,6 +795,7 @@ describe("cloudinary", function () {
       api_key: "1234"
     });
   });
+
   it("should support preloaded identifier format", function () {
     var result = cloudinary.utils.url("raw/private/v123456/document.docx");
     expect(result).to.eql("http://res.cloudinary.com/test123/raw/private/v123456/document.docx");
@@ -804,6 +805,7 @@ describe("cloudinary", function () {
     });
     expect(result).to.eql("http://res.cloudinary.com/test123/image/private/c_scale,w_1.0/v123456/img.jpg");
   });
+
   it("should add responsive width transformation", function () {
     var options, result;
     options = {
@@ -861,4 +863,20 @@ describe("cloudinary", function () {
     result = cloudinary.utils.url("sample.jpg", options);
     expect(result).to.eql('http://res.cloudinary.com/test123/image/upload/s--2hbrSMPO--/sample.jpg');
   });
+
+  it("should not affect user variable names containing predefined names", function() {
+    const options = { transformation: [
+      {
+        $mywidth: "100",
+        $aheight: 300
+      },
+      {
+        width: "3 + $mywidth * 3 + 4 / 2 * initialWidth * $mywidth",
+        height: "3 * initialHeight + $aheight",
+        crop: 'scale'
+      }
+    ]};
+    const result = cloudinary.utils.url("sample", options);
+    expect(result).to.contain("$aheight_300,$mywidth_100/c_scale,h_3_mul_ih_add_$aheight,w_3_add_$mywidth_mul_3_add_4_div_2_mul_iw_mul_$mywidth");
+  });
 });
diff --git a/test/utils/utils_spec.js b/test/utils/utils_spec.js
index d3810d04..6d916839 100644
--- a/test/utils/utils_spec.js
+++ b/test/utils/utils_spec.js
@@ -1061,6 +1061,7 @@ describe("utils", function () {
         t = cloudinary.utils.generate_transformation_string(options);
         expect(t).to.eql("$foo_10/if_fc_gt_2/c_scale,w_$foo_mul_200_div_fc/if_end");
       });
+
       it("should not change variable names even if they look like keywords", function () {
         var options, t;
         options = {
@@ -1076,6 +1077,7 @@ describe("utils", function () {
         t = cloudinary.utils.generate_transformation_string(options);
         expect(t).to.eql("$width_10/w_$width_add_10_add_w");
       });
+
       it("should support text values", function () {
         test_cloudinary_url("sample", {
           effect: "$efname:100",