Index: trunk/src/org/openstreetmap/josm/gui/autofilter/AutoFilterRule.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/autofilter/AutoFilterRule.java	(revision 15842)
+++ trunk/src/org/openstreetmap/josm/gui/autofilter/AutoFilterRule.java	(revision 15843)
@@ -4,4 +4,5 @@
 import java.text.DecimalFormat;
 import java.util.Arrays;
+import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
@@ -148,5 +149,5 @@
                 // #17109, support values like 0.5 or 1.5 - level values are multiplied by 2 when parsing, values are divided by 2 for formatting
                 .setValueExtractor(s -> (int) (Double.parseDouble(s) * 2.))
-                .setValueFormatter(v -> DecimalFormat.getInstance().format(v / 2.)),
+                .setValueFormatter(v -> DecimalFormat.getInstance(Locale.ROOT).format(v / 2.)),
             new AutoFilterRule("layer", 16)
                     .setDefaultValueSupplier(AutoFilterRule::defaultLayer),
Index: trunk/test/unit/org/openstreetmap/josm/gui/autofilter/AutoFilterRuleTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/gui/autofilter/AutoFilterRuleTest.java	(revision 15842)
+++ trunk/test/unit/org/openstreetmap/josm/gui/autofilter/AutoFilterRuleTest.java	(revision 15843)
@@ -6,4 +6,6 @@
 
 import java.util.NoSuchElementException;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 
 import org.junit.Rule;
@@ -42,4 +44,6 @@
         assertTagValuesForPrimitive(level, "way level=10;12-13", 20, 24, 25, 26);
         assertTagValuesForPrimitive(level, "way level=0;0.5;1;1.5;2;2.5;3", 0, 1, 2, 3, 4, 5, 6);
+        assertEquals("0 0.5 1 1.5 2 2.5 3",
+                IntStream.of(0, 1, 2, 3, 4, 5, 6).mapToObj(level::formatValue).collect(Collectors.joining(" ")));
     }