diff --git a/bramble-android/build.gradle b/bramble-android/build.gradle
index d42d0e83b..c989b4b1c 100644
--- a/bramble-android/build.gradle
+++ b/bramble-android/build.gradle
@@ -53,7 +53,7 @@ dependencies {
 	testImplementation "junit:junit:$junit_version"
 	testImplementation "org.jmock:jmock:$jmock_version"
 	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 }
 
 def torBinariesDir = 'src/main/res/raw'
diff --git a/bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java b/bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java
index 2b7b8bb88..cad9fa49c 100644
--- a/bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java
+++ b/bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java
@@ -9,7 +9,7 @@ import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -44,7 +44,7 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 	private AndroidAccountManager accountManager;
 
 	public AndroidAccountManagerTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		app = context.mock(Application.class);
 		applicationInfo = new ApplicationInfo();
 		applicationInfo.dataDir = testDir.getAbsolutePath();
diff --git a/bramble-api/build.gradle b/bramble-api/build.gradle
index 475424044..0cd52e31a 100644
--- a/bramble-api/build.gradle
+++ b/bramble-api/build.gradle
@@ -13,7 +13,6 @@ dependencies {
 	testImplementation "junit:junit:$junit_version"
 	testImplementation "org.jmock:jmock:$jmock_version"
 	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }
diff --git a/bramble-core/build.gradle b/bramble-core/build.gradle
index 8f77f18d2..0d4a255b6 100644
--- a/bramble-core/build.gradle
+++ b/bramble-core/build.gradle
@@ -29,7 +29,7 @@ dependencies {
 	testImplementation "junit:junit:$junit_version"
 	testImplementation "org.jmock:jmock:$jmock_version"
 	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 
 	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
 
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/client/BdfMessageValidatorTest.java b/bramble-core/src/test/java/org/briarproject/bramble/client/BdfMessageValidatorTest.java
index c60bb4fef..4c0bf1418 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/client/BdfMessageValidatorTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/client/BdfMessageValidatorTest.java
@@ -13,7 +13,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.test.ValidatorTestCase;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_CLOCK_DIFFERENCE;
@@ -38,7 +38,7 @@ public class BdfMessageValidatorTest extends ValidatorTestCase {
 	private final Metadata meta = new Metadata();
 
 	public BdfMessageValidatorTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 	}
 
 	@Test(expected = InvalidMessageException.class)
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementProtocolTest.java b/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementProtocolTest.java
index 2541b76b3..5cea40cc7 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementProtocolTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementProtocolTest.java
@@ -11,9 +11,9 @@ import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.jmock.Expectations;
 import org.jmock.auto.Mock;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.jmock.integration.junit4.JUnitRuleMockery;
 import org.jmock.lib.concurrent.Synchroniser;
-import org.jmock.lib.legacy.ClassImposteriser;
 import org.junit.Rule;
 import org.junit.Test;
 
@@ -35,7 +35,7 @@ public class KeyAgreementProtocolTest extends BrambleTestCase {
 	@Rule
 	public JUnitRuleMockery context = new JUnitRuleMockery() {{
 		// So we can mock concrete classes like KeyAgreementTransport
-		setImposteriser(ClassImposteriser.INSTANCE);
+		setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		setThreadingPolicy(new Synchroniser());
 	}};
 
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementTransportTest.java b/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementTransportTest.java
index c5c111c77..d75bf40f4 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementTransportTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/keyagreement/KeyAgreementTransportTest.java
@@ -14,7 +14,7 @@ import org.briarproject.bramble.api.record.RecordWriterFactory;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.CaptureArgumentAction;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import java.io.InputStream;
@@ -58,7 +58,7 @@ public class KeyAgreementTransportTest extends BrambleMockTestCase {
 	private KeyAgreementTransport kat;
 
 	public KeyAgreementTransportTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		inputStream = context.mock(InputStream.class);
 		outputStream = context.mock(OutputStream.class);
 	}
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java b/bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java
index 6c85747ac..82f58436b 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java
@@ -25,7 +25,7 @@ import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.ImmediateExecutor;
 import org.briarproject.bramble.test.RunAction;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -69,7 +69,7 @@ public class PollerImplTest extends BrambleMockTestCase {
 	private PollerImpl poller;
 
 	public PollerImplTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		random = context.mock(SecureRandom.class);
 	}
 
diff --git a/bramble-java/build.gradle b/bramble-java/build.gradle
index f6aeffb92..0f27a3e3e 100644
--- a/bramble-java/build.gradle
+++ b/bramble-java/build.gradle
@@ -27,7 +27,6 @@ dependencies {
 	testImplementation "junit:junit:$junit_version"
 	testImplementation "org.jmock:jmock:$jmock_version"
 	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
 
 	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
 }
diff --git a/briar-android/build.gradle b/briar-android/build.gradle
index 6fb1b3339..9bc421659 100644
--- a/briar-android/build.gradle
+++ b/briar-android/build.gradle
@@ -141,7 +141,7 @@ dependencies {
 	testImplementation "junit:junit:$junit_version"
 	testImplementation "org.jmock:jmock:$jmock_version"
 	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
 
 	androidTestImplementation project(path: ':bramble-api', configuration: 'testOutput')
diff --git a/briar-android/src/test/java/org/briarproject/briar/android/account/SetupViewModelTest.java b/briar-android/src/test/java/org/briarproject/briar/android/account/SetupViewModelTest.java
index e64693789..3cc74b11d 100644
--- a/briar-android/src/test/java/org/briarproject/briar/android/account/SetupViewModelTest.java
+++ b/briar-android/src/test/java/org/briarproject/briar/android/account/SetupViewModelTest.java
@@ -9,7 +9,7 @@ import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.ImmediateExecutor;
 import org.briarproject.briar.android.account.SetupViewModel.State;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Rule;
 import org.junit.Test;
 
@@ -36,7 +36,7 @@ public class SetupViewModelTest extends BrambleMockTestCase {
 	private final DozeHelper dozeHelper;
 
 	public SetupViewModelTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		app = context.mock(Application.class);
 		appContext = context.mock(Context.class);
 		accountManager = context.mock(AccountManager.class);
diff --git a/briar-android/src/test/java/org/briarproject/briar/android/attachment/AttachmentRetrieverTest.java b/briar-android/src/test/java/org/briarproject/briar/android/attachment/AttachmentRetrieverTest.java
index 1b9bdde06..565ddbe0a 100644
--- a/briar-android/src/test/java/org/briarproject/briar/android/attachment/AttachmentRetrieverTest.java
+++ b/briar-android/src/test/java/org/briarproject/briar/android/attachment/AttachmentRetrieverTest.java
@@ -11,7 +11,7 @@ import org.briarproject.briar.api.attachment.Attachment;
 import org.briarproject.briar.api.attachment.AttachmentHeader;
 import org.briarproject.briar.api.attachment.AttachmentReader;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import java.io.ByteArrayInputStream;
@@ -36,7 +36,7 @@ public class AttachmentRetrieverTest extends BrambleMockTestCase {
 	private final AttachmentRetriever retriever;
 
 	public AttachmentRetrieverTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		AttachmentReader attachmentReader =
 				context.mock(AttachmentReader.class);
 		imageSizeCalculator = context.mock(ImageSizeCalculator.class);
diff --git a/briar-android/src/test/java/org/briarproject/briar/android/privategroup/list/GroupListViewModelTest.java b/briar-android/src/test/java/org/briarproject/briar/android/privategroup/list/GroupListViewModelTest.java
index ff96a675d..9e87d2923 100644
--- a/briar-android/src/test/java/org/briarproject/briar/android/privategroup/list/GroupListViewModelTest.java
+++ b/briar-android/src/test/java/org/briarproject/briar/android/privategroup/list/GroupListViewModelTest.java
@@ -26,7 +26,7 @@ import org.briarproject.briar.api.privategroup.event.GroupDissolvedEvent;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationItem;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Rule;
 import org.junit.Test;
 
@@ -95,7 +95,7 @@ public class GroupListViewModelTest extends BrambleMockTestCase {
 			new GroupItem(privateGroup2, authorInfo2, groupCount2, false);
 
 	public GroupListViewModelTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		Application app = context.mock(Application.class);
 		context.checking(new Expectations() {{
 			oneOf(eventBus).addListener(with(any(EventListener.class)));
diff --git a/briar-android/src/test/java/org/briarproject/briar/android/util/UiUtilsFormatDurationTest.java b/briar-android/src/test/java/org/briarproject/briar/android/util/UiUtilsFormatDurationTest.java
index 7d282aae9..6162af3fe 100644
--- a/briar-android/src/test/java/org/briarproject/briar/android/util/UiUtilsFormatDurationTest.java
+++ b/briar-android/src/test/java/org/briarproject/briar/android/util/UiUtilsFormatDurationTest.java
@@ -6,7 +6,7 @@ import android.content.res.Resources;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.briar.R;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import static java.util.concurrent.TimeUnit.DAYS;
@@ -24,7 +24,7 @@ public class UiUtilsFormatDurationTest extends BrambleMockTestCase {
 	private final int strDays = R.plurals.duration_days;
 
 	public UiUtilsFormatDurationTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		ctx = context.mock(Context.class);
 		r = context.mock(Resources.class);
 	}
diff --git a/briar-core/build.gradle b/briar-core/build.gradle
index 9f19fe98a..481c0b5c3 100644
--- a/briar-core/build.gradle
+++ b/briar-core/build.gradle
@@ -25,7 +25,7 @@ dependencies {
 	testImplementation "junit:junit:$junit_version"
 	testImplementation "org.jmock:jmock:$jmock_version"
 	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation "org.jmock:jmock-imposters:$jmock_version"
 
 	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
 
diff --git a/briar-core/src/test/java/org/briarproject/briar/privategroup/invitation/GroupInvitationManagerImplTest.java b/briar-core/src/test/java/org/briarproject/briar/privategroup/invitation/GroupInvitationManagerImplTest.java
index 0e6e9f9e4..183173d65 100644
--- a/briar-core/src/test/java/org/briarproject/briar/privategroup/invitation/GroupInvitationManagerImplTest.java
+++ b/briar-core/src/test/java/org/briarproject/briar/privategroup/invitation/GroupInvitationManagerImplTest.java
@@ -34,7 +34,7 @@ import org.briarproject.briar.api.privategroup.invitation.GroupInvitationRequest
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationResponse;
 import org.jmock.AbstractExpectations;
 import org.jmock.Expectations;
-import org.jmock.lib.legacy.ClassImposteriser;
+import org.jmock.imposters.ByteBuddyClassImposteriser;
 import org.junit.Test;
 
 import java.util.Collection;
@@ -126,7 +126,7 @@ public class GroupInvitationManagerImplTest extends BrambleMockTestCase {
 
 
 	public GroupInvitationManagerImplTest() {
-		context.setImposteriser(ClassImposteriser.INSTANCE);
+		context.setImposteriser(ByteBuddyClassImposteriser.INSTANCE);
 		creatorEngine = context.mock(CreatorProtocolEngine.class);
 		inviteeEngine = context.mock(InviteeProtocolEngine.class);
 		peerEngine = context.mock(PeerProtocolEngine.class);