diff --git a/src/crc64.c b/src/crc64.c
index 8497f5e..1a7f537 100644
--- a/src/crc64.c
+++ b/src/crc64.c
@@ -171,7 +171,7 @@ static const uint64_t crc64_tab[256] = {
 };
 
 
-uint64_t crc64(const unsigned char* s, uint64_t l)
+uint64_t crc64(const char* s, uint64_t l)
 {
 	uint64_t j;
     uint64_t crc = 0;
diff --git a/src/crc64.h b/src/crc64.h
index 7899110..8835f59 100644
--- a/src/crc64.h
+++ b/src/crc64.h
@@ -6,4 +6,4 @@
 
 #include <stdint.h>
 
-uint64_t crc64(const unsigned char* s, uint64_t l);
+uint64_t crc64(const char* s, uint64_t l);