diff --git a/tests/sys/sys/bitstring_test.c b/tests/sys/sys/bitstring_test.c
index edbd2f6c2b2..ac22c36177f 100644
--- a/tests/sys/sys/bitstring_test.c
+++ b/tests/sys/sys/bitstring_test.c
@@ -350,6 +350,8 @@ ATF_TC_BODY(bit_ffs_area, tc)
 	bitstr_t bit_decl(bitstr, nbits);
 	int location;
 
+	memset(bitstr, 0, bitstr_size(nbits));
+
 	bit_set(bitstr, 5);
 	bit_set(bitstr, 6);