diff --git a/src/adler32.c b/src/adler32.c
index f99b2d7..fc4cbed 100644
--- a/src/adler32.c
+++ b/src/adler32.c
@@ -41,12 +41,12 @@
 #define A32_BASE 65521
 #define A32_NMAX 5552
 
-unsigned int tinf_adler32(const void *data, unsigned int length)
+unsigned int tinf_adler32(const void *data, unsigned int length, unsigned int prev_sum /* 1 */)
 {
    const unsigned char *buf = (const unsigned char *)data;
 
-   unsigned int s1 = 1;
-   unsigned int s2 = 0;
+   unsigned int s1 = prev_sum & 0xffff;
+   unsigned int s2 = prev_sum >> 16;
 
    while (length > 0)
    {
diff --git a/src/tinf.h b/src/tinf.h
index e00f171..2d103e0 100644
--- a/src/tinf.h
+++ b/src/tinf.h
@@ -106,7 +106,7 @@ int tinf_gzip_parse_trailer(TINF_GZIP_INFO *gz, const unsigned char **source, un
 int TINFCC tinf_zlib_uncompress(void *dest, unsigned int *destLen,
                                 const void *source, unsigned int sourceLen);
 
-unsigned int TINFCC tinf_adler32(const void *data, unsigned int length);
+unsigned int TINFCC tinf_adler32(const void *data, unsigned int length, unsigned int prev_sum /* 1 */);
 
 unsigned int TINFCC tinf_crc32(const void *data, unsigned int length);