diff --git a/checkin_notes b/checkin_notes
index cfe38d4049..1fea747ca8 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -2729,7 +2729,10 @@ Charlie 29 Apr 2011
         cc_config.cpp
 
 Charlie 1 May 2011
-    - lib: initialize data_dir in CONFIG::defaults().
-
+    - lib: initialize data_dir in CONFIG::defaults(); don't write <data_dir> to 
+        cc_config.xml if empty string, because older versions of BOINC choke.
+    
     lib/
         cc_config.cpp
+
+Charlie 1 May 2011
diff --git a/lib/cc_config.cpp b/lib/cc_config.cpp
index 0a1c98bd3a..1bd86f5ec9 100644
--- a/lib/cc_config.cpp
+++ b/lib/cc_config.cpp
@@ -437,12 +437,15 @@ int CONFIG::write(MIOFILE& out, LOG_FLAGS& log_flags) {
         );
     }
     
+    // Older versions of BOINC choke on empty data_dir string 
+    if (strlen(data_dir)) {
+        out.printf("        <data_dir>%s</data_dir>\n", data_dir);
+    }
+    
     out.printf(
-        "        <data_dir>%s</data_dir>\n"
         "        <disallow_attach>%d</disallow_attach>\n"
         "        <dont_check_file_sizes>%d</dont_check_file_sizes>\n"
         "        <dont_contact_ref_site>%d</dont_contact_ref_site>\n",
-        data_dir,
         disallow_attach,
         dont_check_file_sizes,
         dont_contact_ref_site