diff --git a/modules/pico_fragments.c b/modules/pico_fragments.c
index d5373a38..16049ff8 100644
--- a/modules/pico_fragments.c
+++ b/modules/pico_fragments.c
@@ -441,7 +441,7 @@ void pico_ipv6_process_frag(struct pico_ipv6_exthdr *frag, struct pico_frame *f,
 {
 #if defined(PICO_SUPPORT_IPV6) && defined(PICO_SUPPORT_IPV6FRAG)
     struct pico_frame *first = NULL;
-    struct pico_stack *S = f->dev->stack;
+    struct pico_stack *S;
 
     if (!f || !frag)
     {
@@ -449,6 +449,8 @@ void pico_ipv6_process_frag(struct pico_ipv6_exthdr *frag, struct pico_frame *f,
         return;
     }
 
+    S = f->dev->stack;
+
     first = pico_tree_first(&S->ipv6_fragments);
 
     if (first)