Index: trunk/src/org/openstreetmap/josm/io/CertificateAmendment.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/CertificateAmendment.java	(revision 13699)
+++ trunk/src/org/openstreetmap/josm/io/CertificateAmendment.java	(revision 13701)
@@ -163,4 +163,9 @@
      */
     private static final NativeCertAmend[] PLATFORM_CERT_AMEND = {
+        // Let's Encrypt - should be included in JDK, but problems with Ubuntu 18.04, see #15851
+        new NativeCertAmend("DST Root CA X3", "DST Root CA X3",
+                "DST_Root_CA_X3.pem",
+                "0687260331a72403d909f105e69bcf0d32e1bd2493ffc6d9206d11bcd6770739",
+                "https://acme-v02.api.letsencrypt.org"),
         // Government of Netherlands
         new NativeCertAmend("Staat der Nederlanden Root CA - G2", "Staat der Nederlanden Root CA - G2",