diff --git a/src/main/java/net/sf/jabref/gui/openoffice/OOBibBase.java b/src/main/java/net/sf/jabref/gui/openoffice/OOBibBase.java
index 400f5219ae1..781a16a4cf5 100644
--- a/src/main/java/net/sf/jabref/gui/openoffice/OOBibBase.java
+++ b/src/main/java/net/sf/jabref/gui/openoffice/OOBibBase.java
@@ -1342,6 +1342,10 @@ public int compareTo(ComparableMark other) {
 
         @Override
         public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+
             if (o instanceof ComparableMark) {
                 ComparableMark other = (ComparableMark) o;
                 return (this.position.X == other.position.X) && (this.position.Y == other.position.Y)
diff --git a/src/main/java/net/sf/jabref/importer/ImportFileFilter.java b/src/main/java/net/sf/jabref/importer/ImportFileFilter.java
index 5c42c54cb23..8d2e5d9fe9c 100644
--- a/src/main/java/net/sf/jabref/importer/ImportFileFilter.java
+++ b/src/main/java/net/sf/jabref/importer/ImportFileFilter.java
@@ -73,6 +73,9 @@ public int compareTo(ImportFileFilter o) {
 
     @Override
     public boolean equals(Object o) {
+        if(this == o) {
+            return true;
+        }
         if (o instanceof ImportFileFilter) {
             return name.equals(((ImportFileFilter) o).name);
         }
diff --git a/src/main/java/net/sf/jabref/importer/fileformat/ImportFormat.java b/src/main/java/net/sf/jabref/importer/fileformat/ImportFormat.java
index 3df58101cec..d394f601d2a 100644
--- a/src/main/java/net/sf/jabref/importer/fileformat/ImportFormat.java
+++ b/src/main/java/net/sf/jabref/importer/fileformat/ImportFormat.java
@@ -164,8 +164,8 @@ public int hashCode() {
 
     @Override
     public boolean equals(Object obj) {
-        if(obj == null) {
-            return false;
+        if (this == obj) {
+            return true;
         }
         if(!(obj instanceof ImportFormat)) {
             return false;
diff --git a/src/main/java/net/sf/jabref/logic/groups/ExplicitGroup.java b/src/main/java/net/sf/jabref/logic/groups/ExplicitGroup.java
index 36552f196f6..d204665717e 100644
--- a/src/main/java/net/sf/jabref/logic/groups/ExplicitGroup.java
+++ b/src/main/java/net/sf/jabref/logic/groups/ExplicitGroup.java
@@ -96,6 +96,9 @@ public AbstractGroup deepCopy() {
 
     @Override
     public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
         if (!(o instanceof ExplicitGroup)) {
             return false;
         }
diff --git a/src/main/java/net/sf/jabref/logic/groups/KeywordGroup.java b/src/main/java/net/sf/jabref/logic/groups/KeywordGroup.java
index 72906fb38ae..329e0dd40bb 100644
--- a/src/main/java/net/sf/jabref/logic/groups/KeywordGroup.java
+++ b/src/main/java/net/sf/jabref/logic/groups/KeywordGroup.java
@@ -187,6 +187,9 @@ public Optional<EntriesGroupChange> remove(List<BibEntry> entriesToRemove) {
 
     @Override
     public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
         if (!(o instanceof KeywordGroup)) {
             return false;
         }
diff --git a/src/main/java/net/sf/jabref/logic/groups/SearchGroup.java b/src/main/java/net/sf/jabref/logic/groups/SearchGroup.java
index e2ded390473..9231b635431 100644
--- a/src/main/java/net/sf/jabref/logic/groups/SearchGroup.java
+++ b/src/main/java/net/sf/jabref/logic/groups/SearchGroup.java
@@ -119,6 +119,9 @@ public Optional<EntriesGroupChange> remove(List<BibEntry> entriesToRemove) {
 
     @Override
     public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
         if (!(o instanceof SearchGroup)) {
             return false;
         }
diff --git a/src/main/java/net/sf/jabref/logic/openoffice/CitationEntry.java b/src/main/java/net/sf/jabref/logic/openoffice/CitationEntry.java
index cd27648378c..a13e0bf96d1 100644
--- a/src/main/java/net/sf/jabref/logic/openoffice/CitationEntry.java
+++ b/src/main/java/net/sf/jabref/logic/openoffice/CitationEntry.java
@@ -70,6 +70,9 @@ public int compareTo(CitationEntry other) {
 
     @Override
     public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
         if (o instanceof CitationEntry) {
             CitationEntry other = (CitationEntry) o;
             return this.refMarkName.equals(other.refMarkName);
diff --git a/src/main/java/net/sf/jabref/logic/openoffice/OOBibStyle.java b/src/main/java/net/sf/jabref/logic/openoffice/OOBibStyle.java
index 7d1396c3a5f..a18054eb421 100644
--- a/src/main/java/net/sf/jabref/logic/openoffice/OOBibStyle.java
+++ b/src/main/java/net/sf/jabref/logic/openoffice/OOBibStyle.java
@@ -888,15 +888,21 @@ public int compareTo(OOBibStyle other) {
 
     @Override
     public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
         if (o instanceof OOBibStyle) {
-            return path.equals(((OOBibStyle) o).path);
+            OOBibStyle otherStyle = (OOBibStyle) o;
+            return Objects.equals(path, otherStyle.path) && Objects.equals(name, otherStyle.name)
+                    && Objects.equals(citProperties, otherStyle.citProperties)
+                    && Objects.equals(properties, otherStyle.properties);
         }
         return false;
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(path);
+        return Objects.hash(path, name, citProperties, properties);
     }
 
     private String createAuthorList(String author, int maxAuthors, String andString,
diff --git a/src/main/java/net/sf/jabref/model/entry/CustomEntryType.java b/src/main/java/net/sf/jabref/model/entry/CustomEntryType.java
index 4cce33a174d..e23ecf79ba7 100644
--- a/src/main/java/net/sf/jabref/model/entry/CustomEntryType.java
+++ b/src/main/java/net/sf/jabref/model/entry/CustomEntryType.java
@@ -19,6 +19,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -78,8 +79,11 @@ public int compareTo(EntryType o) {
 
     @Override
     public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
         if (o instanceof CustomEntryType) {
-            return this.compareTo((CustomEntryType) o) == 0;
+            return Objects.equals(name, ((CustomEntryType) o).name);
         } else {
             return false;
         }