diff --git a/app/RunnerException.java b/app/RunnerException.java
index 390d7ef80..200e9abdb 100644
--- a/app/RunnerException.java
+++ b/app/RunnerException.java
@@ -66,6 +66,8 @@ public class RunnerException extends Exception {
    * in each of the constructors above.
    */
   static public final String massage(String msg) {
+    if (msg == null)
+      return "";
     if (msg.indexOf("java.lang.") == 0) {
       //int dot = msg.lastIndexOf('.');
       msg = msg.substring("java.lang.".length());
diff --git a/app/Sizer.java b/app/Sizer.java
index deb837fa5..2b7091c96 100644
--- a/app/Sizer.java
+++ b/app/Sizer.java
@@ -72,7 +72,11 @@ public class Sizer implements MessageConsumer {
         } catch (InterruptedException intExc) { }
       }
     } catch (Exception e) {
-      exception = new RunnerException(e.toString());
+      // The default Throwable.toString() never returns null, but apparently
+      // some sub-class has overridden it to do so, thus we need to check for
+      // it.  See: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1166589459
+      exception = new RunnerException(
+        (e.toString() == null) ? e.getClass().getName() : e.toString());
     }
     
     if (exception != null)