diff --git a/src/main/java/net/tfminecraft/research/util/YamlFolder.java b/src/main/java/net/tfminecraft/research/util/YamlFolder.java
index 87bfb62..283229d 100644
--- a/src/main/java/net/tfminecraft/research/util/YamlFolder.java
+++ b/src/main/java/net/tfminecraft/research/util/YamlFolder.java
@@ -3,10 +3,15 @@
 import java.io.File;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 
 public final class YamlFolder {
 
+    // Sorted so that duplicate ids resolve the same way on every filesystem: the first file by name wins.
+    private static final Comparator<File> BY_NAME = Comparator.comparing(File::getName, String.CASE_INSENSITIVE_ORDER)
+            .thenComparing(File::getName);
+
     private YamlFolder() {}
 
     public static List<File> listYamlFiles(File folder) {
@@ -23,6 +28,7 @@ public static List<File> listYamlFiles(File folder) {
                 yamlFiles.add(file);
             }
         }
+        yamlFiles.sort(BY_NAME);
         return yamlFiles;
     }
 }
diff --git a/src/test/java/net/tfminecraft/research/util/ResearchUtilitiesTest.java b/src/test/java/net/tfminecraft/research/util/ResearchUtilitiesTest.java
index 63ce3f1..597d65c 100644
--- a/src/test/java/net/tfminecraft/research/util/ResearchUtilitiesTest.java
+++ b/src/test/java/net/tfminecraft/research/util/ResearchUtilitiesTest.java
@@ -422,7 +422,7 @@ void yamlFilesAreSelectedOnlyFromReadableDirectories() throws Exception {
         Files.writeString(directory.resolve("other.txt"), "text");
         Files.createDirectory(directory.resolve("folder.yml"));
         assertEquals(List.of(), YamlFolder.listYamlFiles(lower.toFile()));
-        assertEquals(Set.of(lower.toFile(), upper.toFile()), new HashSet<>(YamlFolder.listYamlFiles(directory.toFile())));
+        assertEquals(List.of(lower.toFile(), upper.toFile()), YamlFolder.listYamlFiles(directory.toFile()));
         File unreadable = mock(File.class);
         when(unreadable.exists()).thenReturn(true);
         when(unreadable.isDirectory()).thenReturn(true);
@@ -430,6 +430,26 @@ void yamlFilesAreSelectedOnlyFromReadableDirectories() throws Exception {
         assertEquals(List.of(), YamlFolder.listYamlFiles(unreadable));
     }
 
+    @Test
+    void yamlFilesAreSortedByNameWhateverOrderTheFilesystemLists() {
+        File folder = mock(File.class);
+        when(folder.exists()).thenReturn(true);
+        when(folder.isDirectory()).thenReturn(true);
+        File b = yamlFile("b.yml");
+        File upperA = yamlFile("A.yml");
+        File lowerA = yamlFile("a.yml");
+        File c = yamlFile("C.yml");
+        when(folder.listFiles()).thenReturn(new File[] {c, lowerA, b, upperA});
+        assertEquals(List.of(upperA, lowerA, b, c), YamlFolder.listYamlFiles(folder));
+    }
+
+    private static File yamlFile(String name) {
+        File file = mock(File.class);
+        when(file.isFile()).thenReturn(true);
+        when(file.getName()).thenReturn(name);
+        return file;
+    }
+
     @Test
     void utilityClassesExposeNoPublicConstructors() throws Exception {
         for (Class<?> type : List.of(GridLayout.class, AspectProgressLayout.class, AspectSlotOrder.class,