diff --git a/lslopt/lslparse.py b/lslopt/lslparse.py
index 79caf74..f4acebf 100644
--- a/lslopt/lslparse.py
+++ b/lslopt/lslparse.py
@@ -1674,10 +1674,15 @@ list lazy_list_set(list L, integer i, list v)
                     ]})
 
             if switchcasedefault is None:
-                switchcasedefault = brk
-                self.breakstack[-1][2] = True
-            prelude.append({'nt':'JUMP', 't':None, 'name':switchcasedefault,
-                'scope':blkscope})
+                warning("No 'default:' label in switch statement")
+                if self.brokennodefault:
+                    warning("Broken behaviour active - falling through")
+                if not self.brokennodefault:
+                    switchcasedefault = brk
+                    self.breakstack[-1][2] = True
+            if switchcasedefault is not None:
+                prelude.append({'nt':'JUMP', 't':None, 'name':switchcasedefault,
+                    'scope':blkscope})
             last = self.breakstack.pop()
             if last[2]:
                 blk.append({'nt':'@', 'name':brk, 'scope':blkscope})
@@ -2311,6 +2316,9 @@ list lazy_list_set(list L, integer i, list v)
         if self.enableswitch:
             self.keywords |= frozenset(('switch', 'case', 'break'))
 
+        # Broken behaviour in the absence of a default: label in a switch stmt.
+        self.brokennodefault = 'brokennodefault' in options
+
         # Allow brackets for assignment of list elements e.g. mylist[5]=4
         self.lazylists = 'lazylists' in options
 
diff --git a/main.py b/main.py
index c1ba024..88deec2 100755
--- a/main.py
+++ b/main.py
@@ -228,6 +228,11 @@ Optimizer options (+ means active by default, - means inactive by default):
                        will go to the last label with that name). This flag
                        works around that limitation by replacing the names of
                        the labels in the output with unique ones.
+  brokennodefault    + Mimic Firestorm's legacy broken behaviour when the
+                       'default' label in a switch statement is absent. Rather
+                       than jumping to the end of the switch in that case
+                       (which is how it behaves when this option is not set),
+                       it falls through and executes the first 'case' label.
 
   Deprecated / compatibility syntax extensions options:
 
@@ -300,7 +305,7 @@ def main():
     # Default options
     options = set(('extendedglobalexpr','extendedtypecast','extendedassignment',
         'allowkeyconcat','allowmultistrings','skippreproc','optimize',
-        'optsigns','optfloats','constfold','dcr'
+        'optsigns','optfloats','constfold','dcr', 'brokennodefault',
         ))
 
     try: