diff --git a/lib/cpumask.c b/lib/cpumask.c
index 3389e24..1f71b97 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -109,10 +109,10 @@
 #endif
 	/* FIXME: Bandaid to save us from old primitives which go to NR_CPUS. */
 	if (*mask) {
+		unsigned char *ptr = (unsigned char *)cpumask_bits(*mask);
 		unsigned int tail;
 		tail = BITS_TO_LONGS(NR_CPUS - nr_cpumask_bits) * sizeof(long);
-		memset(cpumask_bits(*mask) + cpumask_size() - tail,
-		       0, tail);
+		memset(ptr + cpumask_size() - tail, 0, tail);
 	}
 
 	return *mask != NULL;