diff --git a/oauth-1.0a.js b/oauth-1.0a.js
index dfdc130..40a2804 100644
--- a/oauth-1.0a.js
+++ b/oauth-1.0a.js
@@ -207,7 +207,20 @@ OAuth.prototype.deParam = function(string) {
         // '' value
         item[1] = item[1] || '';
 
-        data[item[0]] = decodeURIComponent(item[1]);
+        // check if the key already exists
+        // this can occur if the QS part of the url contains duplicate keys like this: ?formkey=formvalue1&formkey=formvalue2
+        if (data[item[0]]){
+          // the key exists already
+          if (!Array.isArray(data[item[0]])) {
+            // replace the value with an array containing the already present value
+            data[item[0]] = [data[item[0]]];
+          }
+          // and add the new found value to it
+          data[item[0]].push(decodeURIComponent(item[1]));
+        } else {
+          // it doesn't exist, just put the found value in the data object
+          data[item[0]] = decodeURIComponent(item[1]);
+        }
     }
 
     return data;
diff --git a/package.json b/package.json
index b88e035..7c95a5f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "oauth-1.0a",
-  "version": "2.2.1",
+  "version": "2.2.2",
   "description": "OAuth 1.0a Request Authorization for Node and Browser.",
   "scripts": {
     "test": "make test"
diff --git a/test/options/multiple_values_qs.js b/test/options/multiple_values_qs.js
new file mode 100644
index 0000000..d92c8fd
--- /dev/null
+++ b/test/options/multiple_values_qs.js
@@ -0,0 +1,50 @@
+var expect = require('chai').expect;
+var OAuth = require('../../oauth-1.0a');
+var crypto = require('crypto');
+
+function hash_function_SHA1(base_string, key) {
+    return crypto.createHmac('sha1', key).update(base_string).digest('base64');
+}
+
+describe("Signature method", function() {
+    describe("HMAC-SHA1 signature method with multiple duplicate values in the querystring", function() {
+        var oauth = new OAuth({
+            consumer: {
+            key: "batch-8f4fd2c6-9fa3-4368-9797-52876d723dd1",
+            secret: "ZACXtYe6LQ4C5X0KbJcDkbW77GYtlaoU"
+            },
+            signature_method: 'HMAC-SHA1',
+            hash_function: hash_function_SHA1
+        });
+
+        //overide for testing only !!!
+        oauth.getTimeStamp = function() {
+            return 1504882975;
+        };
+
+        //overide for testing only !!!
+        oauth.getNonce = function(length) {
+            return 'xsEYfvjTEiPTR3TqJbmhCpUdrDoHF6nk';
+        };
+
+
+        var request_data = {
+          url: "http://localhost:3737/rest/profiles?property=email&value=vel.arcu%40ultriciesornareelit.ca&property=visitdate&value=abc&alt=json",
+          method: "GET"
+        };
+
+        var result = oauth.authorize(request_data);
+
+        it("Signature should match", function() {
+            expect(result.oauth_signature).to.equal("b6nMehqpHnpx0VlZB9IhqFh4Jq0=");
+        });
+
+        it("Nonce should match", function() {
+            expect(result.oauth_nonce).to.equal("xsEYfvjTEiPTR3TqJbmhCpUdrDoHF6nk");
+        });
+
+        it("Timestamp should match", function() {
+            expect(result.oauth_timestamp).to.equal(1504882975);
+        });
+    });
+});
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