diff --git a/jolt-core/src/main/java/com/bazaarvoice/jolt/modifier/function/Strings.java b/jolt-core/src/main/java/com/bazaarvoice/jolt/modifier/function/Strings.java
index 3af56224..243f29e5 100644
--- a/jolt-core/src/main/java/com/bazaarvoice/jolt/modifier/function/Strings.java
+++ b/jolt-core/src/main/java/com/bazaarvoice/jolt/modifier/function/Strings.java
@@ -19,6 +19,7 @@
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 
 @SuppressWarnings( "deprecated" )
 public class Strings {
@@ -47,7 +48,7 @@ protected Optional<String> applySingle( final Object arg ) {
 
             String argString = (String) arg;
 
-            return Optional.of( argString.toUpperCase() );
+            return Optional.of( argString.toUpperCase(Locale.ENGLISH) );
         }
     }
 
@@ -233,4 +234,4 @@ private static Optional<Object> padString( boolean leftPad, String source, List<
 
         return Optional.empty();
     }
-}
\ No newline at end of file
+}