diff --git a/src/mempool.c b/src/mempool.c
index 43696e81..bc1a6587 100644
--- a/src/mempool.c
+++ b/src/mempool.c
@@ -46,6 +46,10 @@ sos_alloc (size_t size)
   char *mem;
 
 #ifdef HAVE_CMPXCHG
+  union {
+    long *lp;
+    char *cp;
+  } u;
   char *old_mem;
 
   size = (size + MAX_ALIGN - 1) & -MAX_ALIGN;
@@ -57,8 +61,9 @@ sos_alloc (size_t size)
       mem += size;
       if (mem >= sos_memory + sizeof (sos_memory))
 	abort ();
+      u.cp = sos_memp;
     }
-  while (cmpxchg_ptr (&sos_memp, old_mem, mem) != old_mem);
+  while (cmpxchg_ptr (&u.lp, old_mem, mem) != old_mem);
 #else
   static pthread_mutex_t sos_lock = PTHREAD_MUTEX_INITIALIZER;
   sigset_t saved_sigmask;