diff --git a/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ParallelRequestsAggregator.java b/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ParallelRequestsAggregator.java
index e8cb078..ba42434 100644
--- a/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ParallelRequestsAggregator.java
+++ b/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ParallelRequestsAggregator.java
@@ -8,6 +8,7 @@ import java.io.OutputStreamWriter;
 import java.io.Writer;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
+import java.util.Locale;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -87,7 +88,7 @@ public class ParallelRequestsAggregator implements CustomAggregator {
 	}
 
 	private void appendTimeAndValue(final StringBuilder builder, final long timeEpochMilli, final int value) {
-		builder.append(String.format("%.3f", timeEpochMilli / 1000.0));
+		builder.append(String.format(Locale.US, "%.3f", timeEpochMilli / 1000.0));
 		builder.append(SEPARATOR);
 		builder.append(value);
 		builder.append(NEWLINE);
diff --git a/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ScatterAggregator.java b/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ScatterAggregator.java
index 2016a9f..5a499db 100644
--- a/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ScatterAggregator.java
+++ b/pdb-plotting/src/main/java/org/lucares/pdb/plot/api/ScatterAggregator.java
@@ -8,6 +8,7 @@ import java.io.OutputStreamWriter;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.util.Formatter;
+import java.util.Locale;
 import java.util.concurrent.TimeUnit;
 
 import org.lucares.collections.Sparse2DLongArray;
@@ -75,7 +76,7 @@ public class ScatterAggregator implements CustomAggregator {
 
         if (useMillis) {
           formattedDateBuilder.delete(0, formattedDateBuilder.length());
-          formatter.format("%.3f", epochMilli / 1000.0);
+          formatter.format(Locale.US, "%.3f", epochMilli / 1000.0);
           formattedDate = formattedDateBuilder.toString();
         } else {
           formattedDate = String.valueOf(epochMilli / 1000);