diff --git a/include/knob.h b/include/knob.h
index 0b4a52c..76bd5c6 100644
--- a/include/knob.h
+++ b/include/knob.h
@@ -1,6 +1,6 @@
 
 #pragma once
 
-#define KNOB_MMAP_SIZE (1UL << 40UL)
+#define KNOB_MMAP_SIZE (1UL << 36UL)
 #define KNOB_ALIGNMENT (sizeof(char*))
 
diff --git a/src/arena.c b/src/arena.c
index c3d92b3..9c1f94f 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -114,7 +114,7 @@ int arena_delete(struct arena *a)
     if (!(a->flags & ARENA_GROW)) {
         return -1;
     }
-    int ok = munmap(a->data, a->cap);
+    int ok = munmap(a->data, KNOB_MMAP_SIZE);
     if (ok == -1) {
         arena_err("munmap");
         return -1;
diff --git a/test/test_arena.c b/test/test_arena.c
index 54e8ea3..2498e37 100644
--- a/test/test_arena.c
+++ b/test/test_arena.c
@@ -98,6 +98,8 @@ int main()
             fprintf(stderr, "arena_delete was supposed to fail, but didn't\n");
             exit(EXIT_FAILURE);
         }
+
+        free(arena_detatch(a));
     }