diff --git a/src/main/java/com/amazonaws/encryptionsdk/internal/RsaJceKeyCipher.java b/src/main/java/com/amazonaws/encryptionsdk/internal/RsaJceKeyCipher.java
index 233cffe37..49c8684dd 100644
--- a/src/main/java/com/amazonaws/encryptionsdk/internal/RsaJceKeyCipher.java
+++ b/src/main/java/com/amazonaws/encryptionsdk/internal/RsaJceKeyCipher.java
@@ -19,6 +19,7 @@
 import java.security.PublicKey;
 import java.security.spec.AlgorithmParameterSpec;
 import java.security.spec.MGF1ParameterSpec;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Logger;
 import java.util.regex.Matcher;
@@ -49,7 +50,7 @@ class RsaJceKeyCipher extends JceKeyCipher {
       final String hashUnknownCase = matcher.group(1);
       if (hashUnknownCase != null) {
         // OAEP mode a.k.a PKCS #1v2
-        final String hash = hashUnknownCase.toUpperCase();
+        final String hash = hashUnknownCase.toUpperCase(Locale.ROOT);
         transformation_ = "RSA/ECB/OAEPPadding";
 
         final MGF1ParameterSpec mgf1Spec;
diff --git a/src/main/java/com/amazonaws/encryptionsdk/jce/JceMasterKey.java b/src/main/java/com/amazonaws/encryptionsdk/jce/JceMasterKey.java
index fc2fe8149..b505c29ea 100644
--- a/src/main/java/com/amazonaws/encryptionsdk/jce/JceMasterKey.java
+++ b/src/main/java/com/amazonaws/encryptionsdk/jce/JceMasterKey.java
@@ -28,6 +28,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
@@ -59,7 +60,7 @@ public static JceMasterKey getInstance(
       final String provider,
       final String keyId,
       final String wrappingAlgorithm) {
-    switch (wrappingAlgorithm.toUpperCase()) {
+    switch (wrappingAlgorithm.toUpperCase(Locale.ROOT)) {
       case "AES/GCM/NOPADDING":
         return new JceMasterKey(provider, keyId, JceKeyCipher.aesGcm(key));
       default:
@@ -82,7 +83,7 @@ public static JceMasterKey getInstance(
       final String provider,
       final String keyId,
       final String wrappingAlgorithm) {
-    if (wrappingAlgorithm.toUpperCase().startsWith("RSA/ECB/")) {
+    if (wrappingAlgorithm.toUpperCase(Locale.ROOT).startsWith("RSA/ECB/")) {
       return new JceMasterKey(
           provider, keyId, JceKeyCipher.rsa(wrappingKey, unwrappingKey, wrappingAlgorithm));
     }
diff --git a/src/main/java/com/amazonaws/encryptionsdk/jce/KeyStoreProvider.java b/src/main/java/com/amazonaws/encryptionsdk/jce/KeyStoreProvider.java
index 57f44aae9..a2bf8725c 100644
--- a/src/main/java/com/amazonaws/encryptionsdk/jce/KeyStoreProvider.java
+++ b/src/main/java/com/amazonaws/encryptionsdk/jce/KeyStoreProvider.java
@@ -36,6 +36,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 /**
@@ -79,7 +80,7 @@ public KeyStoreProvider(
     wrappingAlgorithm_ = wrappingAlgorithm;
     aliasNames_ = Arrays.asList(aliasNames);
     providerName_ = providerName;
-    keyAlgorithm_ = wrappingAlgorithm.split("/", 2)[0].toUpperCase();
+    keyAlgorithm_ = wrappingAlgorithm.split("/", 2)[0].toUpperCase(Locale.ROOT);
   }
 
   /**
diff --git a/src/test/java/com/amazonaws/encryptionsdk/TestVectorRunner.java b/src/test/java/com/amazonaws/encryptionsdk/TestVectorRunner.java
index 8e27eb60d..d32d84dc4 100644
--- a/src/test/java/com/amazonaws/encryptionsdk/TestVectorRunner.java
+++ b/src/test/java/com/amazonaws/encryptionsdk/TestVectorRunner.java
@@ -34,6 +34,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.Callable;
 import java.util.function.Supplier;
@@ -333,7 +334,9 @@ private static <T> TestCase parseTest(
                   transformation += "PKCS1Padding";
                 } else if ("oaep-mgf1".equals(padding)) {
                   final String hashName =
-                      ((String) mkEntry.get("padding-hash")).replace("sha", "sha-").toUpperCase();
+                      ((String) mkEntry.get("padding-hash"))
+                          .replace("sha", "sha-")
+                          .toUpperCase(Locale.ROOT);
                   transformation += "OAEPWith" + hashName + "AndMGF1Padding";
                 } else {
                   throw new IllegalArgumentException("Unsupported padding:" + padding);
@@ -438,7 +441,9 @@ private static TestCase parseTest(
                   transformation += "PKCS1Padding";
                 } else if ("oaep-mgf1".equals(padding)) {
                   final String hashName =
-                      ((String) mkEntry.get("padding-hash")).replace("sha", "sha-").toUpperCase();
+                      ((String) mkEntry.get("padding-hash"))
+                          .replace("sha", "sha-")
+                          .toUpperCase(Locale.ROOT);
                   transformation += "OAEPWith" + hashName + "AndMGF1Padding";
                 } else {
                   throw new IllegalArgumentException("Unsupported padding:" + padding);
@@ -544,7 +549,7 @@ private static Map<String, KeyEntry> parseKeyManifest(final Map<String, Object>
                   name,
                   keyId,
                   keyType,
-                  new SecretKeySpec(Base64.decode(material), algorithm.toUpperCase()));
+                  new SecretKeySpec(Base64.decode(material), algorithm.toUpperCase(Locale.ROOT)));
           break;
         case "private":
           kf = KeyFactory.getInstance(algorithm);
diff --git a/src/test/java/com/amazonaws/encryptionsdk/XCompatDecryptTest.java b/src/test/java/com/amazonaws/encryptionsdk/XCompatDecryptTest.java
index 84d4df574..35d7729ad 100644
--- a/src/test/java/com/amazonaws/encryptionsdk/XCompatDecryptTest.java
+++ b/src/test/java/com/amazonaws/encryptionsdk/XCompatDecryptTest.java
@@ -23,6 +23,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import javax.crypto.spec.SecretKeySpec;
 import org.apache.commons.lang3.StringUtils;
@@ -143,7 +144,7 @@ public static Collection<Object[]> data() throws Exception {
                   + "."
                   + paddingHash;
           String encAlg = (String) aMasterKey.get("encryption_algorithm");
-          switch (encAlg.toUpperCase()) {
+          switch (encAlg.toUpperCase(Locale.ROOT)) {
             case "RSA":
               String cipherBase = "RSA/ECB/";
               String cipherName;
@@ -176,7 +177,7 @@ public static Collection<Object[]> data() throws Exception {
               break;
             default:
               throw new IllegalArgumentException(
-                  "Unknown encryption algorithm: " + encAlg.toUpperCase());
+                  "Unknown encryption algorithm: " + encAlg.toUpperCase(Locale.ROOT));
           }
         }
       }