diff --git a/lib/modules/Sql.pmod/pgsql.pike b/lib/modules/Sql.pmod/pgsql.pike
index bff071042fd4a061f9c6171d4c81d001297a6def..f8b5fed02a90b4de04e590ee412a218f954a78d5 100644
--- a/lib/modules/Sql.pmod/pgsql.pike
+++ b/lib/modules/Sql.pmod/pgsql.pike
@@ -87,7 +87,7 @@ private Thread.Mutex resyncmux;
 protected string _sprintf(int type) {
   string res;
   if (!this)					// Not in destructed objects
-    return "";
+    return UNDEFINED;
   switch(type) {
     case 'O':
       res = sprintf(DRIVERNAME"(%s@%s:%d/%s,%d,%d)",
diff --git a/lib/modules/Sql.pmod/pgsql_util.pmod b/lib/modules/Sql.pmod/pgsql_util.pmod
index e675b162ec183fc40c83ea26b2e8ec98e1c42fda..256f27ddd7fc727122e7d411ffa8df592f266df9 100644
--- a/lib/modules/Sql.pmod/pgsql_util.pmod
+++ b/lib/modules/Sql.pmod/pgsql_util.pmod
@@ -718,14 +718,14 @@ outer:
   private string _sprintf(int type) {
     string res;
     if (!this)					// Not in destructed objects
-      return "";
+      return UNDEFINED;
     switch (type) {
       case 'O':
         int fd = -1;
         if (socket)
           catch(fd = socket->query_fd());
         if (!this)				// Not in destructed objects
-          return "";
+          return UNDEFINED;
         res = predef::sprintf("conxion  fd: %d input queue: %d/%d "
                     "queued portals: %d  output queue: %d/%d\n"
                     "started: %d\n",
@@ -827,7 +827,7 @@ class sql_result {
   protected string _sprintf(int type) {
     string res;
     if (!this)					// Not in destructed objects
-      return "";
+      return UNDEFINED;
     switch (type) {
       case 'O':
         int fd = -1;
@@ -1827,7 +1827,7 @@ class proxy {
   private string _sprintf(int type) {
     string res;
     if (!this)					// Not in destructed objects
-      return "";
+      return UNDEFINED;
     switch (type) {
       case 'O':
         res = sprintf(DRIVERNAME".proxy(%s@%s:%d/%s,%d,%d)",