diff --git a/third_party/blink/renderer/core/svg/svg_tree_scope_resources.cc b/third_party/blink/renderer/core/svg/svg_tree_scope_resources.cc
index 2d2ab9b48ee03d..96f1b7d042c76f 100644
--- a/third_party/blink/renderer/core/svg/svg_tree_scope_resources.cc
+++ b/third_party/blink/renderer/core/svg/svg_tree_scope_resources.cc
@@ -17,10 +17,19 @@ SVGTreeScopeResources::SVGTreeScopeResources(TreeScope* tree_scope)
 LocalSVGResource* SVGTreeScopeResources::ResourceForId(const AtomicString& id) {
   if (id.empty())
     return nullptr;
-  auto& entry = resources_.insert(id, nullptr).stored_value->value;
-  if (!entry)
-    entry = MakeGarbageCollected<LocalSVGResource>(*tree_scope_, id);
-  return entry.Get();
+  // MakeGarbageCollected below may run a synchronous major GC at its
+  // allocation safepoint.  That GC invokes ProcessCustomWeakness(), which can
+  // RemoveAll() dead entries and Shrink() `resources_`, freeing its backing.
+  // Because `resources_` is a PartitionAlloc-backed HashMap (not a
+  // HeapHashMap), the shrink is *not* suppressed by the no-allocation scope
+  // around weak processing.  We therefore must not hold any reference or
+  // iterator into the backing across the allocation.
+  auto it = resources_.find(id);
+  if (it != resources_.end() && it->value)
+    return it->value.Get();
+  auto* resource = MakeGarbageCollected<LocalSVGResource>(*tree_scope_, id);
+  resources_.Set(id, resource);
+  return resource;
 }
 
 LocalSVGResource* SVGTreeScopeResources::ExistingResourceForId(