diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9da117cf0bc..9318eeeb021 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - We added an option to show the preview as an extra tab in the entry editor (instead of in a split view). [#5244](https://github.com/JabRef/jabref/issues/5244)
 - A custom Open/LibreOffice jstyle file now requires a layout line for the entry type `default` [#5452](https://github.com/JabRef/jabref/issues/5452)
 - The entry editor is now open by default when JabRef starts up. [#5460](https://github.com/JabRef/jabref/issues/5460)
+- Customized entry types are now serialized in alphabetical order in the bib file.
 - We added a new ADS fetcher to use the new ADS API [#4949](https://github.com/JabRef/jabref/issues/4949)
 - We added support of the [X11 primary selection](https://unix.stackexchange.com/a/139193/18033) [#2389](https://github.com/JabRef/jabref/issues/2389)
 - We added support to switch between biblatex and bibtex library types. [#5550](https://github.com/JabRef/jabref/issues/5550)
diff --git a/src/main/java/org/jabref/logic/exporter/BibDatabaseWriter.java b/src/main/java/org/jabref/logic/exporter/BibDatabaseWriter.java
index ee643f1ced7..94a8beb41c1 100644
--- a/src/main/java/org/jabref/logic/exporter/BibDatabaseWriter.java
+++ b/src/main/java/org/jabref/logic/exporter/BibDatabaseWriter.java
@@ -7,13 +7,13 @@
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
+import java.util.TreeSet;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -157,7 +157,7 @@ public void savePartOfDatabase(BibDatabaseContext bibDatabaseContext, List<BibEn
         }
 
         // Map to collect entry type definitions that we must save along with entries using them.
-        Set<BibEntryType> typesToWrite = new HashSet<>();
+        Set<BibEntryType> typesToWrite = new TreeSet<>();
 
         // Some file formats write something at the start of the file (like the encoding)
         if (preferences.getSaveType() != SavePreferences.DatabaseSaveType.PLAIN_BIBTEX) {
diff --git a/src/test/java/org/jabref/logic/exporter/BibtexDatabaseWriterTest.java b/src/test/java/org/jabref/logic/exporter/BibtexDatabaseWriterTest.java
index 0ec73d0ceac..f6ee7f5c92b 100644
--- a/src/test/java/org/jabref/logic/exporter/BibtexDatabaseWriterTest.java
+++ b/src/test/java/org/jabref/logic/exporter/BibtexDatabaseWriterTest.java
@@ -287,6 +287,38 @@ void writeEntryWithCustomizedTypeAlsoWritesTypeDeclaration() throws Exception {
                         + "@Comment{jabref-entrytype: customizedtype: req[author;date;title] opt[month;publisher;year]}" + OS.NEWLINE,
                 stringWriter.toString());
     }
+    
+    @Test
+    void writeCustomizedTypesInAlphabeticalOrder() throws Exception {
+        EntryType customizedType = new UnknownEntryType("customizedType");
+        EntryType otherCustomizedType = new UnknownEntryType("otherCustomizedType");
+        BibEntryType customizedBibType = new BibEntryType(
+                customizedType,
+                Collections.singletonList(new BibField(StandardField.TITLE, FieldPriority.IMPORTANT)),
+                Collections.singletonList(new OrFields(StandardField.TITLE)));
+        BibEntryType otherCustomizedBibType = new BibEntryType(
+                otherCustomizedType,
+                Collections.singletonList(new BibField(StandardField.TITLE, FieldPriority.IMPORTANT)),
+                Collections.singletonList(new OrFields(StandardField.TITLE)));
+        entryTypesManager.addCustomOrModifiedType(otherCustomizedBibType, BibDatabaseMode.BIBTEX);
+        entryTypesManager.addCustomOrModifiedType(customizedBibType, BibDatabaseMode.BIBTEX);
+        BibEntry entry = new BibEntry(customizedType);
+        BibEntry otherEntry = new BibEntry(otherCustomizedType);
+        database.insertEntry(otherEntry);
+        database.insertEntry(entry);
+
+        databaseWriter.savePartOfDatabase(bibtexContext, Arrays.asList(entry, otherEntry));
+
+        assertEquals(
+                OS.NEWLINE
+                        + "@Customizedtype{," + OS.NEWLINE + "}" + OS.NEWLINE + OS.NEWLINE
+                        + "@Othercustomizedtype{," + OS.NEWLINE + "}" + OS.NEWLINE + OS.NEWLINE
+                        + "@Comment{jabref-meta: databaseType:bibtex;}"
+                        + OS.NEWLINE + OS.NEWLINE
+                        + "@Comment{jabref-entrytype: customizedtype: req[title] opt[]}" + OS.NEWLINE + OS.NEWLINE
+                        + "@Comment{jabref-entrytype: othercustomizedtype: req[title] opt[]}" + OS.NEWLINE,
+                stringWriter.toString());
+    }
 
     @Test
     void roundtripWithArticleMonths() throws Exception {