diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java
index db454b92b..e422767f0 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileReftableStack.java
@@ -21,6 +21,7 @@
 import java.io.InputStreamReader;
 import java.nio.file.Files;
 import java.nio.file.StandardCopyOption;
+import java.security.SecureRandom;
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;
@@ -65,6 +66,8 @@ private static class StackEntry {
 
 	private final Runnable onChange;
 
+	private final SecureRandom random = new SecureRandom();
+
 	private final Supplier<Config> configSupplier;
 
 	// Used for stats & testing.
@@ -365,8 +368,9 @@ private long nextUpdateIndex() throws IOException {
 	}
 
 	private String filename(long low, long high) {
-		return String.format("%012x-%012x", //$NON-NLS-1$
-				Long.valueOf(low), Long.valueOf(high));
+		return String.format("%012x-%012x-%08x", //$NON-NLS-1$
+				Long.valueOf(low), Long.valueOf(high),
+				random.nextInt());
 	}
 
 	/**