diff --git a/processor/src/test/java/org/mapstruct/ap/test/builtin/DatatypeFactoryTest.java b/processor/src/test/java/org/mapstruct/ap/test/builtin/DatatypeFactoryTest.java
index fe52452c7..17d7980ff 100644
--- a/processor/src/test/java/org/mapstruct/ap/test/builtin/DatatypeFactoryTest.java
+++ b/processor/src/test/java/org/mapstruct/ap/test/builtin/DatatypeFactoryTest.java
@@ -10,7 +10,10 @@ import java.text.SimpleDateFormat;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.GregorianCalendar;
+import java.util.TimeZone;
 
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mapstruct.ap.test.builtin.bean.CalendarProperty;
@@ -34,6 +37,19 @@ import static org.assertj.core.api.Assertions.assertThat;
 @RunWith(AnnotationProcessorTestRunner.class)
 public class DatatypeFactoryTest {
 
+    private TimeZone originalTimeZone;
+
+    @Before
+    public void setUp() {
+        originalTimeZone = TimeZone.getDefault();
+        TimeZone.setDefault( TimeZone.getTimeZone( "Europe/Berlin" ) );
+    }
+
+    @After
+    public void tearDown() {
+        TimeZone.setDefault( originalTimeZone );
+    }
+
     @Test
     public void testNoConflictsWithOwnDatatypeFactory() throws ParseException {
 
diff --git a/processor/src/test/java/org/mapstruct/ap/test/conversion/date/DateConversionTest.java b/processor/src/test/java/org/mapstruct/ap/test/conversion/date/DateConversionTest.java
index c7a3cf331..43ed5b330 100644
--- a/processor/src/test/java/org/mapstruct/ap/test/conversion/date/DateConversionTest.java
+++ b/processor/src/test/java/org/mapstruct/ap/test/conversion/date/DateConversionTest.java
@@ -16,6 +16,7 @@ import java.util.GregorianCalendar;
 import java.util.List;
 import java.util.Locale;
 
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -40,11 +41,19 @@ import org.mapstruct.ap.testutil.runner.EnabledOnCompiler;
 @RunWith(AnnotationProcessorTestRunner.class)
 public class DateConversionTest {
 
+    private Locale originalLocale;
+
     @Before
     public void setDefaultLocale() {
+        originalLocale = Locale.getDefault();
         Locale.setDefault( Locale.GERMAN );
     }
 
+    @After
+    public void tearDown() {
+        Locale.setDefault( originalLocale );
+    }
+
     @Test
     @DisabledOnCompiler(Compiler.JDK11)
     // See https://bugs.openjdk.java.net/browse/JDK-8211262, there is a difference in the default formats on Java 9+
diff --git a/processor/src/test/java/org/mapstruct/ap/test/conversion/java8time/Java8TimeConversionTest.java b/processor/src/test/java/org/mapstruct/ap/test/conversion/java8time/Java8TimeConversionTest.java
index 573e300bf..25ed95886 100644
--- a/processor/src/test/java/org/mapstruct/ap/test/conversion/java8time/Java8TimeConversionTest.java
+++ b/processor/src/test/java/org/mapstruct/ap/test/conversion/java8time/Java8TimeConversionTest.java
@@ -17,6 +17,8 @@ import java.util.Calendar;
 import java.util.Date;
 import java.util.TimeZone;
 
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mapstruct.ap.testutil.IssueKey;
@@ -33,6 +35,18 @@ import static org.assertj.core.api.Assertions.assertThat;
 @IssueKey("121")
 public class Java8TimeConversionTest {
 
+    private TimeZone originalTimeZone;
+
+    @Before
+    public void setUp() {
+        originalTimeZone = TimeZone.getDefault();
+    }
+
+    @After
+    public void tearDown() {
+        TimeZone.setDefault( originalTimeZone );
+    }
+
     @Test
     public void testDateTimeToString() {
         Source src = new Source();
diff --git a/processor/src/test/java/org/mapstruct/ap/test/conversion/jodatime/JodaConversionTest.java b/processor/src/test/java/org/mapstruct/ap/test/conversion/jodatime/JodaConversionTest.java
index 30c96395b..db61b85bc 100644
--- a/processor/src/test/java/org/mapstruct/ap/test/conversion/jodatime/JodaConversionTest.java
+++ b/processor/src/test/java/org/mapstruct/ap/test/conversion/jodatime/JodaConversionTest.java
@@ -16,6 +16,7 @@ import org.joda.time.DateTimeZone;
 import org.joda.time.LocalDate;
 import org.joda.time.LocalDateTime;
 import org.joda.time.LocalTime;
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -36,11 +37,19 @@ import org.mapstruct.ap.testutil.runner.EnabledOnCompiler;
 @IssueKey("75")
 public class JodaConversionTest {
 
+    private Locale originalLocale;
+
     @Before
     public void setDefaultLocale() {
+        originalLocale = Locale.getDefault();
         Locale.setDefault( Locale.GERMAN );
     }
 
+    @After
+    public void tearDown() {
+        Locale.setDefault( originalLocale );
+    }
+
     @Test
     public void testDateTimeToString() {
         Source src = new Source();
diff --git a/processor/src/test/java/org/mapstruct/ap/test/conversion/numbers/NumberFormatConversionTest.java b/processor/src/test/java/org/mapstruct/ap/test/conversion/numbers/NumberFormatConversionTest.java
index ad2caecfd..9b92182f6 100644
--- a/processor/src/test/java/org/mapstruct/ap/test/conversion/numbers/NumberFormatConversionTest.java
+++ b/processor/src/test/java/org/mapstruct/ap/test/conversion/numbers/NumberFormatConversionTest.java
@@ -5,6 +5,7 @@
  */
 package org.mapstruct.ap.test.conversion.numbers;
 
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -30,11 +31,19 @@ import static org.assertj.core.api.Assertions.entry;
 @RunWith(AnnotationProcessorTestRunner.class)
 public class NumberFormatConversionTest {
 
+    private Locale originalLocale;
+
     @Before
     public void setDefaultLocale() {
+        originalLocale = Locale.getDefault();
         Locale.setDefault( Locale.ENGLISH );
     }
 
+    @After
+    public void tearDown() {
+        Locale.setDefault( originalLocale );
+    }
+
     @Test
     public void shouldApplyStringConversions() {
         Source source = new Source();
diff --git a/processor/src/test/java/org/mapstruct/ap/test/nestedmethodcall/NestedMappingMethodInvocationTest.java b/processor/src/test/java/org/mapstruct/ap/test/nestedmethodcall/NestedMappingMethodInvocationTest.java
index 11ac637f9..3738f5628 100644
--- a/processor/src/test/java/org/mapstruct/ap/test/nestedmethodcall/NestedMappingMethodInvocationTest.java
+++ b/processor/src/test/java/org/mapstruct/ap/test/nestedmethodcall/NestedMappingMethodInvocationTest.java
@@ -20,6 +20,7 @@ import javax.xml.datatype.DatatypeFactory;
 import javax.xml.datatype.XMLGregorianCalendar;
 import javax.xml.namespace.QName;
 
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -38,11 +39,19 @@ public class NestedMappingMethodInvocationTest {
 
     public static final QName QNAME = new QName( "dont-care" );
 
+    private Locale originalLocale;
+
     @Before
     public void setDefaultLocale() {
+        originalLocale = Locale.getDefault();
         Locale.setDefault( Locale.GERMAN );
     }
 
+    @After
+    public void tearDown() {
+        Locale.setDefault( originalLocale );
+    }
+
     @Test
     @WithClasses( {
         OrderTypeToOrderDtoMapper.class,