diff --git a/bramble-api/src/main/java/org/briarproject/bramble/util/PrivacyUtils.java b/bramble-api/src/main/java/org/briarproject/bramble/util/PrivacyUtils.java
index c39fc5e86..25d23c2ae 100644
--- a/bramble-api/src/main/java/org/briarproject/bramble/util/PrivacyUtils.java
+++ b/bramble-api/src/main/java/org/briarproject/bramble/util/PrivacyUtils.java
@@ -6,6 +6,7 @@ import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
+import java.util.Locale;
 
 import javax.annotation.Nullable;
 
@@ -51,7 +52,7 @@ public class PrivacyUtils {
 	}
 
 	private static String scrubIpv6Address(byte[] ipv6) {
-		String hex = toHexString(ipv6).toLowerCase();
+		String hex = toHexString(ipv6).toLowerCase(Locale.US);
 		return hex.substring(0, 2) + "[scrubbed]" + hex.substring(30);
 	}
 
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoComponentImpl.java b/bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoComponentImpl.java
index 1bb7fe9f8..5dd24a5f7 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoComponentImpl.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/crypto/CryptoComponentImpl.java
@@ -34,6 +34,7 @@ import java.security.NoSuchAlgorithmException;
 import java.security.Provider;
 import java.security.SecureRandom;
 import java.security.Security;
+import java.util.Locale;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
@@ -500,7 +501,7 @@ class CryptoComponentImpl implements CryptoComponent {
 		arraycopy(publicKey, 0, address, 0, publicKey.length);
 		arraycopy(checksum, 0, address, publicKey.length, ONION_CHECKSUM_BYTES);
 		address[address.length - 1] = ONION_HS_PROTOCOL_VERSION;
-		return Base32.encode(address).toLowerCase();
+		return Base32.encode(address).toLowerCase(Locale.US);
 	}
 
 }
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/contact/PendingContactFactoryImplTest.java b/bramble-core/src/test/java/org/briarproject/bramble/contact/PendingContactFactoryImplTest.java
index 879bd5db1..4f4747300 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/contact/PendingContactFactoryImplTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/contact/PendingContactFactoryImplTest.java
@@ -13,6 +13,7 @@ import org.jmock.Expectations;
 import org.junit.Test;
 
 import java.security.GeneralSecurityException;
+import java.util.Locale;
 
 import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.BASE32_LINK_BYTES;
@@ -174,7 +175,7 @@ public class PendingContactFactoryImplTest extends BrambleMockTestCase {
 		rawLink[0] = (byte) formatVersion;
 		byte[] publicKeyBytes = publicKey.getEncoded();
 		arraycopy(publicKeyBytes, 0, rawLink, 1, publicKeyBytes.length);
-		String base32 = Base32.encode(rawLink).toLowerCase();
+		String base32 = Base32.encode(rawLink).toLowerCase(Locale.US);
 		assertEquals(BASE32_LINK_BYTES, base32.length());
 		return base32;
 	}
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/crypto/OnionEncodingTest.java b/bramble-core/src/test/java/org/briarproject/bramble/crypto/OnionEncodingTest.java
new file mode 100644
index 000000000..2574b7f53
--- /dev/null
+++ b/bramble-core/src/test/java/org/briarproject/bramble/crypto/OnionEncodingTest.java
@@ -0,0 +1,30 @@
+package org.briarproject.bramble.crypto;
+
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.briarproject.bramble.test.TestSecureRandomProvider;
+import org.junit.Test;
+
+import java.security.SecureRandom;
+import java.util.regex.Pattern;
+
+import static org.junit.Assert.assertTrue;
+
+public class OnionEncodingTest extends BrambleTestCase {
+
+	private static final Pattern ONION_V3 = Pattern.compile("[a-z2-7]{56}");
+
+	private final CryptoComponent crypto =
+			new CryptoComponentImpl(new TestSecureRandomProvider(), null);
+	private final SecureRandom secureRandom = new SecureRandom();
+
+	@Test
+	public void testHostnameIsValid() {
+		byte[] publicKey = new byte[32];
+		for (int i = 0; i < 100; i++) {
+			secureRandom.nextBytes(publicKey);
+			String onion = crypto.encodeOnion(publicKey);
+			assertTrue(onion, ONION_V3.matcher(onion).matches());
+		}
+	}
+}
diff --git a/briar-core/src/test/java/org/briarproject/briar/test/BriarTestUtils.java b/briar-core/src/test/java/org/briarproject/briar/test/BriarTestUtils.java
index 6d50b08ac..cd1b7c20c 100644
--- a/briar-core/src/test/java/org/briarproject/briar/test/BriarTestUtils.java
+++ b/briar-core/src/test/java/org/briarproject/briar/test/BriarTestUtils.java
@@ -11,6 +11,8 @@ import org.briarproject.bramble.util.Base32;
 import org.briarproject.briar.api.client.MessageTracker;
 import org.briarproject.briar.api.client.MessageTracker.GroupCount;
 
+import java.util.Locale;
+
 import static java.lang.System.arraycopy;
 import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.FORMAT_VERSION;
 import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.RAW_LINK_BYTES;
@@ -52,7 +54,7 @@ public class BriarTestUtils {
 		byte[] publicKey = keyPair.getPublic().getEncoded();
 		linkBytes[0] = FORMAT_VERSION;
 		arraycopy(publicKey, 0, linkBytes, 1, RAW_LINK_BYTES - 1);
-		return ("briar://" + Base32.encode(linkBytes)).toLowerCase();
+		return ("briar://" + Base32.encode(linkBytes)).toLowerCase(Locale.US);
 	}
 
 }
diff --git a/briar-headless/src/main/java/org/briarproject/bramble/identity/OutputAuthor.kt b/briar-headless/src/main/java/org/briarproject/bramble/identity/OutputAuthor.kt
index baff61c9a..0d82b24a0 100644
--- a/briar-headless/src/main/java/org/briarproject/bramble/identity/OutputAuthor.kt
+++ b/briar-headless/src/main/java/org/briarproject/bramble/identity/OutputAuthor.kt
@@ -3,6 +3,7 @@ package org.briarproject.bramble.identity
 import org.briarproject.bramble.api.identity.Author
 import org.briarproject.briar.api.identity.AuthorInfo
 import org.briarproject.briar.headless.json.JsonDict
+import java.util.Locale
 
 fun Author.output() = JsonDict(
     "formatVersion" to formatVersion,
@@ -11,4 +12,4 @@ fun Author.output() = JsonDict(
     "publicKey" to publicKey.encoded
 )
 
-fun AuthorInfo.Status.output() = name.toLowerCase()
+fun AuthorInfo.Status.output() = name.lowercase(Locale.US)
diff --git a/briar-headless/src/main/java/org/briarproject/briar/headless/blogs/OutputBlogPost.kt b/briar-headless/src/main/java/org/briarproject/briar/headless/blogs/OutputBlogPost.kt
index 9f6e22b0c..7283174eb 100644
--- a/briar-headless/src/main/java/org/briarproject/briar/headless/blogs/OutputBlogPost.kt
+++ b/briar-headless/src/main/java/org/briarproject/briar/headless/blogs/OutputBlogPost.kt
@@ -4,6 +4,7 @@ import org.briarproject.bramble.identity.output
 import org.briarproject.briar.api.blog.BlogPostHeader
 import org.briarproject.briar.api.blog.MessageType
 import org.briarproject.briar.headless.json.JsonDict
+import java.util.Locale
 
 internal fun BlogPostHeader.output(text: String) = JsonDict(
     "text" to text,
@@ -18,4 +19,4 @@ internal fun BlogPostHeader.output(text: String) = JsonDict(
     "timestampReceived" to timeReceived
 )
 
-internal fun MessageType.output() = name.toLowerCase()
+internal fun MessageType.output() = name.lowercase(Locale.US)