Index: src/exceptions.c
===================================================================
--- src/exceptions.c	(revision 38496)
+++ src/exceptions.c	(working copy)
@@ -37,6 +37,10 @@
         __attribute__nonnull__(1)
         __attribute__nonnull__(3);
 
+PARROT_DOES_NOT_RETURN
+static void die_from_null_exception(PARROT_INTERP)
+        __attribute__nonnull__(1);
+
 PARROT_CAN_RETURN_NULL
 static opcode_t * pass_exception_args(PARROT_INTERP,
     ARGIN(const char *sig),
@@ -51,6 +55,8 @@
 #define ASSERT_ARGS_build_exception_from_args __attribute__unused__ int _ASSERT_ARGS_CHECK = \
        PARROT_ASSERT_ARG(interp) \
     || PARROT_ASSERT_ARG(format)
+#define ASSERT_ARGS_die_from_null_exception __attribute__unused__ int _ASSERT_ARGS_CHECK = \
+       PARROT_ASSERT_ARG(interp)
 #define ASSERT_ARGS_pass_exception_args __attribute__unused__ int _ASSERT_ARGS_CHECK = \
        PARROT_ASSERT_ARG(interp) \
     || PARROT_ASSERT_ARG(sig) \
@@ -201,6 +207,8 @@
 {
     ASSERT_ARGS(Parrot_ex_throw_from_op)
     opcode_t   *address;
+    if(PMC_IS_NULL(exception) || exception->vtable->base_type != enum_class_Exception)
+        die_from_null_exception(interp);
     PMC * const handler = Parrot_cx_find_handler_local(interp, exception);
     if (PMC_IS_NULL(handler)) {
         STRING * const message     = VTABLE_get_string(interp, exception);
@@ -461,7 +469,7 @@
 {
     ASSERT_ARGS(Parrot_ex_rethrow_from_op)
     if (exception->vtable->base_type != enum_class_Exception)
-        PANIC(interp, "Illegal rethrow");
+        die_from_null_exception(interp);
 
     Parrot_ex_mark_unhandled(interp, exception);
 
@@ -753,7 +761,26 @@
     DUMPCORE();
 }
 
+/*
 
+=item C<static void die_from_null_exception(PARROT_INTERP)>
+
+Somebody has tried to throw a null exception. This is a fatal error. Print
+an error message and exit.
+
+=cut
+
+*/
+
+PARROT_DOES_NOT_RETURN
+static void
+die_from_null_exception(PARROT_INTERP)
+{
+    fprintf(stderr, "FATAL: Attempt to throw a NULL PMC\n");
+    Parrot_exit(interp, 255);
+}
+
+
 /*
 
 =back