diff --git a/engine/src/main/java/org/hibernate/search/engine/impl/ImmutableSearchFactory.java b/engine/src/main/java/org/hibernate/search/engine/impl/ImmutableSearchFactory.java
index a480577e969..b9998139d6f 100644
--- a/engine/src/main/java/org/hibernate/search/engine/impl/ImmutableSearchFactory.java
+++ b/engine/src/main/java/org/hibernate/search/engine/impl/ImmutableSearchFactory.java
@@ -6,6 +6,7 @@
  */
 package org.hibernate.search.engine.impl;
 
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
@@ -167,7 +168,7 @@ private ObjectLookupMethod determineDefaultObjectLookupMethod() {
 		}
 		else {
 			try {
-				return Enum.valueOf( ObjectLookupMethod.class, objectLookupMethod.toUpperCase() );
+				return Enum.valueOf( ObjectLookupMethod.class, objectLookupMethod.toUpperCase( Locale.ROOT ) );
 			}
 			catch (IllegalArgumentException e) {
 				throw log.invalidPropertyValue( objectLookupMethod, Environment.OBJECT_LOOKUP_METHOD );
@@ -182,7 +183,7 @@ private DatabaseRetrievalMethod determineDefaultDatabaseRetrievalMethod() {
 		}
 		else {
 			try {
-				return Enum.valueOf( DatabaseRetrievalMethod.class, databaseRetrievalMethod.toUpperCase() );
+				return Enum.valueOf( DatabaseRetrievalMethod.class, databaseRetrievalMethod.toUpperCase( Locale.ROOT ) );
 			}
 			catch (IllegalArgumentException e) {
 				throw log.invalidPropertyValue( databaseRetrievalMethod, Environment.OBJECT_LOOKUP_METHOD );
diff --git a/engine/src/main/java/org/hibernate/search/store/impl/DirectoryProviderHelper.java b/engine/src/main/java/org/hibernate/search/store/impl/DirectoryProviderHelper.java
index 25b79c438c6..729ccb36fb0 100644
--- a/engine/src/main/java/org/hibernate/search/store/impl/DirectoryProviderHelper.java
+++ b/engine/src/main/java/org/hibernate/search/store/impl/DirectoryProviderHelper.java
@@ -10,6 +10,7 @@
 import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
+import java.util.Locale;
 import java.util.Properties;
 
 import org.apache.lucene.store.FSDirectory;
@@ -268,7 +269,7 @@ public static FSDirectoryType getType(Properties properties) {
 			String fsDirectoryTypeValue = properties.getProperty( FS_DIRECTORY_TYPE_PROP_NAME );
 			if ( StringHelper.isNotEmpty( fsDirectoryTypeValue ) ) {
 				try {
-					fsDirectoryType = Enum.valueOf( FSDirectoryType.class, fsDirectoryTypeValue.toUpperCase() );
+					fsDirectoryType = Enum.valueOf( FSDirectoryType.class, fsDirectoryTypeValue.toUpperCase( Locale.ROOT ) );
 				}
 				catch (IllegalArgumentException e) {
 					throw new SearchException( "Invalid option value for " + FS_DIRECTORY_TYPE_PROP_NAME + ": " + fsDirectoryTypeValue );