diff -up webkitgtk-2.20.3/Source/JavaScriptCore/runtime/HashMapImpl.h.memset_zero_length webkitgtk-2.20.3/Source/JavaScriptCore/runtime/HashMapImpl.h
--- webkitgtk-2.20.3/Source/JavaScriptCore/runtime/HashMapImpl.h.memset_zero_length	2018-02-19 08:45:16.000000000 +0100
+++ webkitgtk-2.20.3/Source/JavaScriptCore/runtime/HashMapImpl.h	2018-06-26 09:29:58.672408600 +0200
@@ -220,7 +220,10 @@ public:
 
     ALWAYS_INLINE void reset(uint32_t capacity)
     {
-        memset(this, -1, allocationSize(capacity));
+#if COMPILER(GCC_OR_CLANG) && defined(_FORTIFY_SOURCE)
+        if (capacity && allocationSize(capacity))
+#endif
+            memset(this, -1, allocationSize(capacity));
     }
 };