diff --git a/modules/appnexusBidAdapter.js b/modules/appnexusBidAdapter.js
index 3f0bf3a4826..1480bc164b5 100644
--- a/modules/appnexusBidAdapter.js
+++ b/modules/appnexusBidAdapter.js
@@ -157,32 +157,6 @@ function newRenderer(adUnitCode, rtbBid, rendererOptions = {}) {
   return renderer;
 }
 
-/* Turn keywords parameter into ut-compatible format */
-function getKeywords(keywords) {
-  let arrs = [];
-
-  utils._each(keywords, (v, k) => {
-    if (utils.isArray(v)) {
-      let values = [];
-      utils._each(v, (val) => {
-        val = utils.getValueString('keywords.' + k, val);
-        if (val) { values.push(val); }
-      });
-      v = values;
-    } else {
-      v = utils.getValueString('keywords.' + k, v);
-      if (utils.isStr(v)) {
-        v = [v];
-      } else {
-        return;
-      } // unsuported types - don't send a key
-    }
-    arrs.push({key: k, value: v});
-  });
-
-  return arrs;
-}
-
 /**
  * Unpack the Server's Bid into a Prebid-compatible one.
  * @param serverBid
@@ -310,7 +284,7 @@ function bidToTag(bid) {
     tag.external_imp_id = bid.params.externalImpId;
   }
   if (!utils.isEmpty(bid.params.keywords)) {
-    tag.keywords = getKeywords(bid.params.keywords);
+    tag.keywords = utils.transformBidderParamKeywords(bid.params.keywords);
   }
 
   if (bid.mediaType === NATIVE || utils.deepAccess(bid, `mediaTypes.${NATIVE}`)) {
diff --git a/modules/prebidServerBidAdapter.js b/modules/prebidServerBidAdapter.js
index fff1331e572..6533d9d00ee 100644
--- a/modules/prebidServerBidAdapter.js
+++ b/modules/prebidServerBidAdapter.js
@@ -208,7 +208,8 @@ const paramTypes = {
   'appnexus': {
     'member': tryConvertString,
     'invCode': tryConvertString,
-    'placementId': tryConvertNumber
+    'placementId': tryConvertNumber,
+    'keywords': utils.transformBidderParamKeywords
   },
   'rubicon': {
     'accountId': tryConvertNumber,
@@ -503,7 +504,7 @@ const OPEN_RTB_PROTOCOL = {
 
       // get bidder params in form { <bidder code>: {...params} }
       const ext = adUnit.bids.reduce((acc, bid) => {
-        // TODO: move this bidder specific out to a more ideal location (submodule?); issue# pending
+        // TODO: move this bidder specific out to a more ideal location (submodule?); https://github.com/prebid/Prebid.js/issues/2420
         // convert all AppNexus keys to underscore format for pbs
         if (bid.bidder === 'appnexus') {
           bid.params.use_pmt_rule = (typeof bid.params.usePaymentRule === 'boolean') ? bid.params.usePaymentRule : false;
diff --git a/src/utils.js b/src/utils.js
index 678f61de87e..5675ace6bf8 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -1046,3 +1046,36 @@ export function isInteger(value) {
 export function convertCamelToUnderscore(value) {
   return value.replace(/(?:^|\.?)([A-Z])/g, function (x, y) { return '_' + y.toLowerCase() }).replace(/^_/, '');
 }
+
+/**
+ * Converts an object of arrays (either strings or numbers) into an array of objects containing key and value properties
+ * normally read from bidder params
+ * eg { foo: ['bar', 'baz'], fizz: ['buzz'] }
+ * becomes [{ key: 'foo', value: ['bar', 'baz']}, {key: 'fizz', value: ['buzz']}]
+ * @param {Object{Arrays}} keywords object of arrays representing keyvalue pairs
+ * @param {string} paramName name of parent object (eg 'keywords') containing keyword data, used in error handling
+ */
+export function transformBidderParamKeywords(keywords, paramName = 'keywords') {
+  let arrs = [];
+
+  exports._each(keywords, (v, k) => {
+    if (exports.isArray(v)) {
+      let values = [];
+      exports._each(v, (val) => {
+        val = exports.getValueString(paramName + '.' + k, val);
+        if (val) { values.push(val); }
+      });
+      v = values;
+    } else {
+      v = exports.getValueString(paramName + '.' + k, v);
+      if (exports.isStr(v)) {
+        v = [v];
+      } else {
+        return;
+      } // unsuported types - don't send a key
+    }
+    arrs.push({key: k, value: v});
+  });
+
+  return arrs;
+}
diff --git a/test/spec/modules/prebidServerBidAdapter_spec.js b/test/spec/modules/prebidServerBidAdapter_spec.js
index d528c9a3191..b155d61d8e5 100644
--- a/test/spec/modules/prebidServerBidAdapter_spec.js
+++ b/test/spec/modules/prebidServerBidAdapter_spec.js
@@ -347,7 +347,11 @@ describe('S2S Adapter', () => {
             'bidder': 'appnexus',
             'params': {
               'placementId': '10433394',
-              'member': 123
+              'member': 123,
+              'keywords': {
+                'foo': ['bar', 'baz'],
+                'fizz': ['buzz']
+              }
             },
             'bid_id': '123',
             'adUnitCode': 'div-gpt-ad-1460505748561-0',
@@ -598,7 +602,7 @@ describe('S2S Adapter', () => {
       const s2sConfig = Object.assign({}, CONFIG, {
         endpoint: 'https://prebid.adnxs.com/pbs/v1/openrtb2/auction'
       });
-      config.setConfig({s2sConfig});
+      config.setConfig({s2sConfig: s2sConfig});
 
       const aliasBidder = {
         bidder: 'brealtime',
@@ -625,7 +629,7 @@ describe('S2S Adapter', () => {
       const s2sConfig = Object.assign({}, CONFIG, {
         endpoint: 'https://prebid.adnxs.com/pbs/v1/openrtb2/auction'
       });
-      config.setConfig({s2sConfig});
+      config.setConfig({s2sConfig: s2sConfig});
 
       const alias = 'foobar';
       const aliasBidder = {
@@ -655,10 +659,14 @@ describe('S2S Adapter', () => {
       const s2sConfig = Object.assign({}, CONFIG, {
         endpoint: 'https://prebid.adnxs.com/pbs/v1/openrtb2/auction'
       });
-      config.setConfig({s2sConfig});
+      config.setConfig({s2sConfig: s2sConfig});
 
       const myRequest = utils.deepClone(REQUEST);
       myRequest.ad_units[0].bids[0].params.usePaymentRule = true;
+      myRequest.ad_units[0].bids[0].params.keywords = {
+        foo: ['bar', 'baz'],
+        fizz: ['buzz']
+      };
 
       adapter.callBids(myRequest, BID_REQUESTS, addBidResponse, done, ajax);
       const requestBid = JSON.parse(requests[0].requestBody);
@@ -667,6 +675,34 @@ describe('S2S Adapter', () => {
       expect(requestBid.imp[0].ext.appnexus.placement_id).to.exist.and.to.equal(10433394);
       expect(requestBid.imp[0].ext.appnexus.use_pmt_rule).to.exist.and.to.be.true;
       expect(requestBid.imp[0].ext.appnexus.member).to.exist;
+      expect(requestBid.imp[0].ext.appnexus.keywords).to.exist.and.to.deep.equal([{
+        key: 'foo',
+        value: ['bar', 'baz']
+      }, {
+        key: 'fizz',
+        value: ['buzz']
+      }]);
+
+      config.resetConfig();
+      const oldS2sConfig = Object.assign({}, CONFIG);
+      config.setConfig({s2sConfig: oldS2sConfig});
+
+      const myRequest2 = utils.deepClone(REQUEST);
+      myRequest2.ad_units[0].bids[0].params.keywords = {
+        foo: ['bar', 'baz'],
+        fizz: ['buzz']
+      };
+
+      adapter.callBids(myRequest2, BID_REQUESTS, addBidResponse, done, ajax);
+      const requestBid2 = JSON.parse(requests[1].requestBody);
+
+      expect(requestBid2.ad_units[0].bids[0].params.keywords).to.exist.and.to.deep.equal([{
+        key: 'foo',
+        value: ['bar', 'baz']
+      }, {
+        key: 'fizz',
+        value: ['buzz']
+      }]);
     });
   });