diff --git a/src/main/java/it/unibz/inf/isochrone/db/Database.java b/src/main/java/it/unibz/inf/isochrone/db/Database.java
index 1a572ee4095c3493a5d200c20e34d60a3042902e..a80d93982f5809d36b43c4d5655fe898e076c933 100644
--- a/src/main/java/it/unibz/inf/isochrone/db/Database.java
+++ b/src/main/java/it/unibz/inf/isochrone/db/Database.java
@@ -783,6 +783,10 @@ public class Database {
 	 * @return a string with the placeholders plugged in to a statement.
 	 */
 	private static String calculatePlaceHolders(final int length) {
+		if (length <= 0) {
+			return "";
+		}
+
 		final StringBuilder builder = new StringBuilder((2 * length) - 1);
 		builder.append("?");