diff --git a/CHANGELOG.md b/CHANGELOG.md
index bdcbfa43487..12f856d00cf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,7 +27,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - We fixed an error in the CrossRef fetcher that occurred if one of the fetched entries had no title
 - We fixed an issue that prevented new entries to be automatically assigned to the currently selected group [#2783](https://github.com/JabRef/jabref/issues/2783).
 - We fixed a bug that only allowed parsing positive timezones from a FileAnnotation [#2839](https://github.com/JabRef/jabref/issues/22839)
-
+- We fixed a bug that did not allow the correct re-export of the MS-Office XML field `msbib-accessed` with a different date format [#2859](https://github.com/JabRef/jabref/issues/2859).
 
 ### Removed
 
diff --git a/src/main/java/org/jabref/logic/msbib/MSBibEntry.java b/src/main/java/org/jabref/logic/msbib/MSBibEntry.java
index 7e1cb3d2758..2155ee5a56f 100644
--- a/src/main/java/org/jabref/logic/msbib/MSBibEntry.java
+++ b/src/main/java/org/jabref/logic/msbib/MSBibEntry.java
@@ -10,6 +10,7 @@
 
 import org.jabref.model.entry.Author;
 import org.jabref.model.entry.AuthorList;
+import org.jabref.model.entry.Date;
 import org.jabref.model.strings.StringUtil;
 
 import org.w3c.dom.Document;
@@ -26,14 +27,6 @@
  */
 class MSBibEntry {
 
-    /**
-     * Allows 20.3-2007|||20/3-  2007 etc.
-     * <b>(\d{1,2})\s?[.,-/]\s?(\d{1,2})\s?[.,-/]\s?(\d{2,4})</b>
-     * 1-2 DIGITS SPACE SEPERATOR SPACE 1-2 DIGITS SPACE SEPERATOR SPACE 2-4 DIGITS
-     */
-    private static final Pattern DATE_PATTERN = Pattern
-            .compile("(\\d{1,2})\\s*[.,-/]\\s*(\\d{1,2})\\s*[.,-/]\\s*(\\d{2,4})");
-
     // MSBib fields and values
     public Map<String, String> fields = new HashMap<>();
     public List<MsBibAuthor> authors;
@@ -165,22 +158,11 @@ private void populateFromXml(Element entry) {
         String dayAccessed = getXmlElementTextContent("DayAccessed", entry);
         String yearAccessed = getXmlElementTextContent("YearAccessed", entry);
 
-        StringBuilder sbDateAccesed = new StringBuilder();
-        if (monthAccessed != null) {
-            sbDateAccesed.append(monthAccessed);
-            sbDateAccesed.append(' ');
-        }
-        if (dayAccessed != null) {
-            sbDateAccesed.append(dayAccessed);
-            sbDateAccesed.append(", ");
-        }
-        if (yearAccessed != null) {
-            sbDateAccesed.append(yearAccessed);
-        }
-        dateAccessed = sbDateAccesed.toString().trim();
-        if (dateAccessed.isEmpty() || ",".equals(dateAccessed)) {
-            dateAccessed = null;
-        }
+        Optional<Date> parsedDateAcessed = Date.parse(Optional.ofNullable(yearAccessed),
+                Optional.ofNullable(monthAccessed),
+                Optional.ofNullable(dayAccessed));
+
+        parsedDateAcessed.map(Date::getNormalized).ifPresent(date -> dateAccessed = date);
 
         NodeList nodeLst = entry.getElementsByTagNameNS("*", "Author");
         if (nodeLst.getLength() > 0) {
@@ -262,15 +244,7 @@ public Element getEntryDom(Document document) {
             addField(document, rootNode, entry.getKey(), entry.getValue());
         }
 
-        // based on bibtex content
-        if (dateAccessed != null) {
-            Matcher matcher = DATE_PATTERN.matcher(dateAccessed);
-            if (matcher.matches() && (matcher.groupCount() >= 3)) {
-                addField(document, rootNode, "Month" + "Accessed", matcher.group(1));
-                addField(document, rootNode, "Day" + "Accessed", matcher.group(2));
-                addField(document, rootNode, "Year" + "Accessed", matcher.group(3));
-            }
-        }
+        Optional.ofNullable(dateAccessed).ifPresent(field -> addDateAcessedFields(document, rootNode));
 
         Element allAuthors = document.createElementNS(MSBibDatabase.NAMESPACE, MSBibDatabase.PREFIX + "Author");
 
@@ -361,6 +335,23 @@ private void addAuthor(Document document, Element allAuthors, String entryName,
 
     }
 
+    private void addDateAcessedFields(Document document, Element rootNode) {
+        Optional<Date> parsedDateAcesseField = Date.parse(dateAccessed);
+        parsedDateAcesseField.flatMap(Date::getYear).map(accYear -> accYear.toString()).ifPresent(yearAccessed -> {
+            addField(document, rootNode, "Year" + "Accessed", yearAccessed);
+        });
+
+        parsedDateAcesseField.flatMap(Date::getMonth)
+                .map(accMonth -> accMonth.getTwoDigitNumber()).ifPresent(monthAcessed -> {
+                    addField(document, rootNode, "Month" + "Accessed", monthAcessed);
+
+                });
+        parsedDateAcesseField.flatMap(Date::getDay).map(accDay -> accDay.toString()).ifPresent(dayAccessed -> {
+            addField(document, rootNode, "Day" + "Accessed", dayAccessed);
+        });
+
+    }
+
     private void addAddress(Document document, Element parent, String addressToSplit) {
         if (addressToSplit == null) {
             return;
diff --git a/src/main/java/org/jabref/model/entry/Date.java b/src/main/java/org/jabref/model/entry/Date.java
index 5b4db035bfd..08bb3d7f552 100644
--- a/src/main/java/org/jabref/model/entry/Date.java
+++ b/src/main/java/org/jabref/model/entry/Date.java
@@ -31,21 +31,25 @@ public Date(TemporalAccessor date) {
      * The code is essentially taken from http://stackoverflow.com/questions/4024544/how-to-parse-dates-in-multiple-formats-using-simpledateformat.
      */
     public static Optional<Date> parse(String dateString) {
-        List<String> formatStrings = Arrays.asList("uuuu-M-d", "uuuu-M", "d-M-uuuu", "M/uu", "M/uuuu", "MMMM d, uuuu", "MMMM, uuuu",
+        Objects.requireNonNull(dateString);
+        List<String> formatStrings = Arrays.asList("uuuu-M-d", "uuuu-M", "d-M-uuuu", "M/uu", "M/uuuu", "MMMM d, uuuu",
+                "MMMM, uuuu",
                 "d.M.uuuu", "uuuu.M.d", "uuuu");
-        for (String formatString : formatStrings) {
-            try {
-                TemporalAccessor parsedDate = DateTimeFormatter.ofPattern(formatString).parse(dateString);
-                return Optional.of(new Date(parsedDate));
-            } catch (DateTimeParseException ignored) {
-                // Ignored
+
+            for (String formatString : formatStrings) {
+                try {
+                    TemporalAccessor parsedDate = DateTimeFormatter.ofPattern(formatString).parse(dateString);
+                    return Optional.of(new Date(parsedDate));
+                } catch (DateTimeParseException ignored) {
+                    // Ignored
+                }
             }
-        }
 
         return Optional.empty();
     }
 
-    public static Optional<Date> parse(Optional<String> yearValue, Optional<String> monthValue, Optional<String> dayValue) {
+    public static Optional<Date> parse(Optional<String> yearValue, Optional<String> monthValue,
+            Optional<String> dayValue) {
         Optional<Year> year = yearValue.flatMap(Date::convertToInt).map(Year::of);
         Optional<Month> month = monthValue.flatMap(Month::parse);
         Optional<Integer> day = dayValue.flatMap(Date::convertToInt);
@@ -107,8 +111,12 @@ public TemporalAccessor toTemporalAccessor() {
 
     @Override
     public boolean equals(Object o) {
-        if (this == o) return true;
-        if (o == null || getClass() != o.getClass()) return false;
+        if (this == o) {
+            return true;
+        }
+        if ((o == null) || (getClass() != o.getClass())) {
+            return false;
+        }
         Date date1 = (Date) o;
         return Objects.equals(getYear(), date1.getYear()) &&
                 Objects.equals(getMonth(), date1.getMonth()) &&
diff --git a/src/test/java/org/jabref/model/entry/DateTest.java b/src/test/java/org/jabref/model/entry/DateTest.java
index 5c55cc92179..3192ef78554 100644
--- a/src/test/java/org/jabref/model/entry/DateTest.java
+++ b/src/test/java/org/jabref/model/entry/DateTest.java
@@ -14,4 +14,9 @@ public void parseCorrectlyDayMonthYearDate() throws Exception {
         Date expected = new Date(LocalDate.of(2014, 6, 19));
         assertEquals(Optional.of(expected), Date.parse("19-06-2014"));
     }
+
+    @Test(expected = NullPointerException.class)
+    public void parseDateNull() {
+        assertEquals(Optional.empty(), Date.parse(null));
+    }
 }
diff --git a/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTest1.xml b/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTest1.xml
index 960fd22d6b3..d92aaaa3a05 100644
--- a/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTest1.xml
+++ b/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTest1.xml
@@ -24,8 +24,8 @@
 <b:NumberVolumes>10</b:NumberVolumes>
 <b:AbbreviatedCaseNumber>abb</b:AbbreviatedCaseNumber>
 <b:BIBTEX_Size>1000</b:BIBTEX_Size>
-<b:MonthAccessed>12</b:MonthAccessed>
-<b:DayAccessed>10</b:DayAccessed>
+<b:MonthAccessed>10</b:MonthAccessed>
+<b:DayAccessed>12</b:DayAccessed>
 <b:YearAccessed>2015</b:YearAccessed>
 <b:Day>5</b:Day>
 <b:Author/>
diff --git a/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTestDateAcessed.bib b/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTestDateAcessed.bib
new file mode 100644
index 00000000000..bc4edda355f
--- /dev/null
+++ b/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTestDateAcessed.bib
@@ -0,0 +1,12 @@
+% Encoding: UTF-8
+
+@Article{Testa,
+  author         = {Sam and jason},
+  title          = {Test},
+  journaltitle   = {Test},
+  year           = {2012},
+  date           = {2016},
+  msbib-accessed = {2015-12-12},
+}
+
+@Comment{jabref-meta: databaseType:biblatex;}
diff --git a/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTestDateAcessed.xml b/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTestDateAcessed.xml
new file mode 100644
index 00000000000..03524e8a072
--- /dev/null
+++ b/src/test/resources/org/jabref/logic/exporter/MsBibExportFormatTestDateAcessed.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<b:Sources xmlns:b="http://schemas.openxmlformats.org/officeDocument/2006/bibliography" xmlns="http://schemas.openxmlformats.org/officeDocument/2006/bibliography" SelectedStyle="">
+<b:Source>
+<b:Year>2012</b:Year>
+<b:BIBTEX_Entry>article</b:BIBTEX_Entry>
+<b:SourceType>JournalArticle</b:SourceType>
+<b:Accessed>2015-12-12</b:Accessed>
+<b:Title>Test</b:Title>
+<b:Tag>Testa</b:Tag>
+<b:YearAccessed>2015</b:YearAccessed>
+<b:MonthAccessed>12</b:MonthAccessed>
+<b:DayAccessed>12</b:DayAccessed>
+<b:Author>
+<b:Author>
+<b:NameList>
+<b:Person>
+<b:Last>Sam</b:Last>
+</b:Person>
+<b:Person>
+<b:Last>jason</b:Last>
+</b:Person>
+</b:NameList>
+</b:Author>
+</b:Author>
+<b:JournalName>Test</b:JournalName>
+</b:Source>
+</b:Sources>