diff --git a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/DatePOSIXFunctions.java b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/DatePOSIXFunctions.java
index eca5e1ac88bf3af2009e7bed1b779032c454e98a..e807bbea6f6f5d7157f74dcc6026367316fe54ae 100644
--- a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/DatePOSIXFunctions.java
+++ b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/base/DatePOSIXFunctions.java
@@ -582,7 +582,8 @@ public class DatePOSIXFunctions {
                          * future version the default century inferred from a 2-digit year will
                          * change’.
                          */
-                        throw RInternalError.unimplemented();
+                        builder.appendPattern("yy");
+                        break;
                     case 'Y':
                         /*
                          * Year with century. Note that whereas there was no zero in the original