diff --git a/src/sm9_alg.c b/src/sm9_alg.c
index 8eba8378..efdb4c5d 100644
--- a/src/sm9_alg.c
+++ b/src/sm9_alg.c
@@ -1071,18 +1071,14 @@ void sm9_fp12_pow(sm9_fp12_t r, const sm9_fp12_t a, const sm9_bn_t k)
 {
 	char kbits[257];
 	sm9_fp12_t t;
-	int i = 0;
+	int i;
 
 	assert(sm9_bn_cmp(k, SM9_P_MINUS_ONE) < 0);
 	sm9_fp12_set_zero(t);
 
 	sm9_bn_to_bits(k, kbits);
-	sm9_fp12_copy(t, a);
-	while (kbits[i] == '0') {
-		i++;
-	}
-	i++;
-	for (; i < 256; i++) {
+	sm9_fp12_set_one(t);
+	for (i = 1; i < 256; i++) {
 		sm9_fp12_sqr(t, t);
 		if (kbits[i] == '1') {
 			sm9_fp12_mul(t, t, a);