--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -2189,16 +2189,19 @@ ArenaList::pickArenasToRelocate()
     // we can move into existing arenas, and we choose the least full areans to
     // relocate.
     //
     // This is made easier by the fact that the arena list has been sorted in
     // descending order of number of used cells, so we will always relocate a
     // tail of the arena list. All we need to do is find the point at which to
     // start relocating.
 
+    if (isCursorAtEnd())
+        return nullptr;
+
     ArenaHeader **arenap = cursorp_;               // Next arena to consider
     size_t previousFreeCells = 0;                  // Count of free cells before
     size_t followingUsedCells = countUsedCells();  // Count of used cells after
     mozilla::DebugOnly<size_t> lastFreeCells(0);
     size_t cellsPerArena = Arena::thingsPerArena((*arenap)->getThingSize());
 
     while (*arenap) {
         ArenaHeader *arena = *arenap;