diff --git a/core/alloc.c b/core/alloc.c
index b61ffc3..c838bfb 100644
--- a/core/alloc.c
+++ b/core/alloc.c
@@ -192,7 +192,11 @@ int freeFromSlab(void *ptr, struct slabEntry *slab)
                 if ((slabEntry->page <= (vaddr_t)ptr) &&
                     ((vaddr_t)ptr < (slabEntry->page + PAGE_SIZE))) {
                         // pr_devel("free place! was %d is now %d\n", slabEntry->freeEl, ptr);
-                        *((vaddr_t *)ptr) = (vaddr_t)slabEntry->freeEl;
+                        if (slabEntry->full) {
+                                *((vaddr_t *)ptr) = (vaddr_t)NULL;
+                        } else {
+                                *((vaddr_t *)ptr) = (vaddr_t)slabEntry->freeEl;
+                        }
                         slabEntry->freeEl = ptr;
                         slabEntry->full   = 0;
                         return 1;