diff --git a/backends/xnnpack/runtime/XNNWeightsCache.cpp b/backends/xnnpack/runtime/XNNWeightsCache.cpp
index 54191b72825..7767c65285a 100644
--- a/backends/xnnpack/runtime/XNNWeightsCache.cpp
+++ b/backends/xnnpack/runtime/XNNWeightsCache.cpp
@@ -206,9 +206,18 @@ size_t XNNWeightsCache::look_up_or_insert(
     size_t size) {
   size_t offset = context->look_up(context, cache_key);
 
+  // XNNPACK can call this with ptr==nullptr when it previously hit the cache
+  // and skipped packing. We can't validate against the ptr contents in this
+  // case, so just return the offset. This might actually be a bug in XNNPACK
+  // since calling look_up_or_insert with ptr==nullptr doesn't really make
+  // sense...
+  if (ptr == nullptr) {
+    return offset;
+  }
+
   if (offset != SIZE_MAX) {
     void* saved_ptr = context->offset_to_addr(context, offset);
-    if (0 == memcmp(ptr, saved_ptr, size)) {
+    if (saved_ptr != nullptr && 0 == memcmp(ptr, saved_ptr, size)) {
       return offset;
     }
     // Failure, cache is out of date