diff --git a/src/algo_sha1.c b/src/algo_sha1.c
index 42ca94cf..dbf646b8 100644
--- a/src/algo_sha1.c
+++ b/src/algo_sha1.c
@@ -69,7 +69,7 @@ typedef union _BYTE64QUAD16 {
 } BYTE64QUAD16;
 
 /* Hash a single 512-bit block. This is the core of the algorithm. */
-void SHA1_Transform(sha1_quadbyte state[5], sha1_byte buffer[64]) {
+void SHA1_Transform(sha1_quadbyte state[5], const sha1_byte buffer[64]) {
     sha1_quadbyte a, b, c, d, e;
     BYTE64QUAD16 src;
     BYTE64QUAD16 *block;
@@ -127,7 +127,7 @@ void SHA1_Init(SHA_CTX* context) {
 }
 
 /* Run your data through this. */
-void SHA1_Update(SHA_CTX *context, sha1_byte *data, unsigned int len) {
+void SHA1_Update(SHA_CTX *context, const sha1_byte *data, unsigned int len) {
     unsigned int i, j;
 
     j = (context->count[0] >> 3) & 63;
diff --git a/src/algo_sha1.h b/src/algo_sha1.h
index 8c3ec35c..d8b44379 100644
--- a/src/algo_sha1.h
+++ b/src/algo_sha1.h
@@ -44,6 +44,7 @@ extern "C" {
 #ifdef HAVE_INTTYPES_H
 # include <inttypes.h>
 #endif
+#include <sys/types.h>
 
 /* Make sure you define these types for your architecture: */
 typedef uint32_t sha1_quadbyte;         /* 4 byte type */
@@ -63,7 +64,7 @@ typedef struct _SHA_CTX {
 
 #ifndef NOPROTO
 void SHA1_Init(SHA_CTX *context);
-void SHA1_Update(SHA_CTX *context, sha1_byte *data, unsigned int len);
+void SHA1_Update(SHA_CTX *context, const sha1_byte *data, unsigned int len);
 void SHA1_Final(sha1_byte digest[SHA1_DIGEST_LENGTH], SHA_CTX *context);
 /*(added for lighttpd)*/
 unsigned char *SHA1(const unsigned char *d, size_t n, unsigned char *md);