diff --git a/tinycrypt/ecc.c b/tinycrypt/ecc.c
index ee91957..3407aaf 100644
--- a/tinycrypt/ecc.c
+++ b/tinycrypt/ecc.c
@@ -424,9 +424,13 @@
 	}
 
 	digit = vli[num_digits - 1];
+#if defined __GNUC__ || defined __clang__ || defined __CC_ARM
+	i = uECC_WORD_BITS - __builtin_clz(digit);
+#else
 	for (i = 0; digit; ++i) {
 		digit >>= 1;
 	}
+#endif
 
 	return (((bitcount_t)(num_digits - 1) << uECC_WORD_BITS_SHIFT) + i);
 }