diff --git a/extmod/uzlib/adler32.c b/extmod/uzlib/adler32.c
index b06a7b37c..1f1759493 100644
--- a/extmod/uzlib/adler32.c
+++ b/extmod/uzlib/adler32.c
@@ -41,7 +41,7 @@
 #define A32_BASE 65521
 #define A32_NMAX 5552
 
-unsigned int uzlib_adler32(const void *data, unsigned int length, unsigned int prev_sum /* 1 */)
+uint32_t uzlib_adler32(const void *data, unsigned int length, uint32_t prev_sum /* 1 */)
 {
    const unsigned char *buf = (const unsigned char *)data;
 
diff --git a/extmod/uzlib/crc32.c b/extmod/uzlib/crc32.c
index 8c9976594..e24c643b6 100644
--- a/extmod/uzlib/crc32.c
+++ b/extmod/uzlib/crc32.c
@@ -46,7 +46,7 @@ static const unsigned int tinf_crc32tab[16] = {
 };
 
 /* crc is previous value for incremental computation, 0xffffffff initially */
-unsigned int uzlib_crc32(const void *data, unsigned int length, unsigned int crc)
+uint32_t uzlib_crc32(const void *data, unsigned int length, uint32_t crc)
 {
    const unsigned char *buf = (const unsigned char *)data;
    unsigned int i;