diff --git a/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/BarChartAggregator.java b/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/BarChartAggregator.java
index d2132d8..447b8e6 100644
--- a/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/BarChartAggregator.java
+++ b/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/BarChartAggregator.java
@@ -82,7 +82,7 @@ public class BarChartAggregator implements CustomAggregator, IndexedAggregator,
 
     @Override
     public String renderLabels(final GnuplotAxis xAxis) {
-        return String.format("set label at %s %f, %d '%s' center front offset 0,0.3", // front
+        return String.format(Locale.US, "set label at %s %f, %d '%s' center front offset 0,0.3", // front
                 xAxis == GnuplotAxis.X1 ? "first" : "second", //
                 getIndex() + 0.5, //
                 getCount(), //