diff --git a/common/src/main/java/ctbrec/recorder/postprocessing/CreateContactSheet.java b/common/src/main/java/ctbrec/recorder/postprocessing/CreateContactSheet.java
index a8b22873..574cfac0 100644
--- a/common/src/main/java/ctbrec/recorder/postprocessing/CreateContactSheet.java
+++ b/common/src/main/java/ctbrec/recorder/postprocessing/CreateContactSheet.java
@@ -6,6 +6,7 @@ import java.io.IOException;
 import java.nio.file.Files;
 import java.text.MessageFormat;
 import java.util.Arrays;
+import java.util.Locale;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -47,13 +48,15 @@ public class CreateContactSheet extends AbstractPlaceholderAwarePostProcessor {
         long lengthInSeconds = rec.getLength().getSeconds();
         double thumbnailInterval = lengthInSeconds / (double)numberOfThumbs;
 
-        String filterArg = MessageFormat.format("fps=1/{0},scale={4}:-1,tile={1}x{2}:color={6}:margin={3}:padding={3},scale={5}:-1",
+        MessageFormat mf = new MessageFormat("fps=1/{0},scale={4}:-1,tile={1}x{2}:color={6}:margin={3}:padding={3},scale={5}:-1", Locale.ENGLISH);
+        String filterArg = mf.format(new Object[] {
                 thumbnailInterval,
                 cols, rows,
                 padding,
                 Integer.toString(thumbWidth),
                 Integer.toString(totalWidth),
-                color);
+                color},
+                new StringBuffer(), null).toString();
         File executionDir = rec.getPostProcessedFile().isDirectory() ? rec.getPostProcessedFile() : rec.getPostProcessedFile().getParentFile();
         File output = new File(executionDir, filename);