diff --git a/js/src/jit-test/tests/basic/regress-bug720680.js b/js/src/jit-test/tests/basic/regress-bug720680.js
new file mode 100644
index 00000000000..ebb794fb545
--- /dev/null
+++ b/js/src/jit-test/tests/basic/regress-bug720680.js
@@ -0,0 +1,15 @@
+// |jit-test| error: InternalError
+version(0);
+eval("\
+function TimeFromYear( y ) {}\
+addTestCase( -2208988800000 );\
+function addTestCase( t ) {\
+  var start = TimeFromYear((addTestCase(addTestCase << t, 0)));\
+    new TestCase( \
+                  SECTION,\
+                  '(new Date('+d+')).getUTCDay()',\
+                  WeekDay((d)),\
+                  (new Date(let ({ stop } = 'properties.length' )('/ab[c\\\n]/'))).getUTCDay() \
+                );\
+}\
+");
diff --git a/js/src/jsopcode.cpp b/js/src/jsopcode.cpp
index 4c25af71ae6..43c6f08611d 100644
--- a/js/src/jsopcode.cpp
+++ b/js/src/jsopcode.cpp
@@ -855,8 +855,7 @@ Sprinter::put(const char *s, size_t len)
             s = stringAt(s - oldBase);  /* this is where it lives now */
         memmove(bp, s, len);
     } else {
-        JS_ASSERT(s < base || s >= base + size);
-        memcpy(bp, s, len);
+        js_memcpy(bp, s, len);
     }
 
     bp[len] = 0;
@@ -2059,7 +2058,7 @@ DecompileDestructuringLHS(SprintStack *ss, jsbytecode *pc, jsbytecode *endpc, JS
          * the nb parameter.
          */
         ptrdiff_t todo = ss->sprinter.getOffset();
-        ss->sprinter.setOffset(todo + PAREN_SLOP);
+        ss->sprinter.reserve(PAREN_SLOP);
         pc = Decompile(ss, pc, -((intN)ss->top));
         if (!pc)
             return NULL;