diff --git a/src/backend/model/fileaccess/MetadataLoader.ts b/src/backend/model/fileaccess/MetadataLoader.ts
index bb5e07b3..03e09543 100644
--- a/src/backend/model/fileaccess/MetadataLoader.ts
+++ b/src/backend/model/fileaccess/MetadataLoader.ts
@@ -197,23 +197,35 @@ export class MetadataLoader {
 
     //function to convert timestamp into milliseconds taking offset into account
     const timestampToMS = (timestamp: string, offset: string) => {
-      "replace first two : with - in timestamp string and add offset if exists (else +00:00 - UTC), parse this into MS"
-      return Date.parse(timestamp.replace(':', '-').replace(':', '-') + (offset ? offset : '+00:00'));
+      if (!timestamp) {
+        return undefined;
+      }
+      //replace : with - in the yyyy-mm-dd part of the timestamp.
+      let formattedTimestamp = timestamp.substring(0,9).replaceAll(':', '-') + timestamp.substring(9,timestamp.length);
+      if (formattedTimestamp.indexOf("Z") > 0) { //replace Z (and what comes after the Z) with offset
+        formattedTimestamp.substring(0, formattedTimestamp.indexOf("Z")) + (offset ? offset : '+00:00');
+      } else if (formattedTimestamp.indexOf("+") > 0) { //don't do anything
+      } else { //add offset
+        formattedTimestamp = formattedTimestamp + (offset ? offset : '+00:00');
+      }
+      //parse into MS and return
+      return Date.parse(formattedTimestamp);
     }
 
     //function to calculate offset from exif.exif.gpsTimeStamp or exif.gps.GPSDateStamp + exif.gps.GPSTimestamp
     const getTimeOffsetByGPSStamp = (timestamp: string, gpsTimeStamp: string, gps: any) => {
-      let UTCTimestamp = gpsTimeStamp; //use the exif.exif.gpsTimestamp if available
+      let UTCTimestamp = gpsTimeStamp;
       if (!UTCTimestamp &&
         gps &&
         gps.GPSDateStamp &&
         gps.GPSTimeStamp) { //else use exif.gps.GPS*Stamp if available
         //GPS timestamp is always UTC (+00:00)
-        UTCTimestamp = gps.GPSDateStamp.replaceAll(':', '-') + gps.GPSTimeStamp.join(':') + '+00:00';
+        UTCTimestamp = gps.GPSDateStamp.replaceAll(':', '-') + gps.GPSTimeStamp.join(':');
       }
-      if (UTCTimestamp) {
+      if (UTCTimestamp && timestamp) {
         //offset in minutes is the difference between gps timestamp and given timestamp
-        const offsetMinutes = (Date.parse(UTCTimestamp) - Date.parse(timestamp.replace(':', '-').replace(':', '-'))) / 1000 / 60;
+        //to calculate this correctly, we have to work with the same offset
+        const offsetMinutes = (timestampToMS(timestamp, '+00:00')- timestampToMS(UTCTimestamp, '+00:00')) / 1000 / 60;
         if (-720 <= offsetMinutes && offsetMinutes <= 840) {
           //valid offset is within -12 and +14 hrs (https://en.wikipedia.org/wiki/List_of_UTC_offsets)
           return (offsetMinutes < 0 ? "-" : "+") +                              //leading +/-
diff --git a/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.jpg b/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.jpg
index f1c9a652..18433139 100644
Binary files a/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.jpg and b/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.jpg differ
diff --git a/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.json b/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.json
index e5f78368..7a231aeb 100644
--- a/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.json
+++ b/test/backend/assets/timestamps/sydney_opera_house_no_tsoffset_but_gps_utc.json
@@ -5,7 +5,7 @@
   },
   "creationDate": 1600512957000,
   "creationDateOffset": "+10:00",
-  "fileSize": 22653,
+  "fileSize": 22641,
   "cameraData": {
     "model": "ILCE-7RM3",
     "make": "Sony"