diff --git a/include/libtorrent/sha1.hpp b/include/libtorrent/sha1.hpp
index 74b74ba5d..c22c5087c 100644
--- a/include/libtorrent/sha1.hpp
+++ b/include/libtorrent/sha1.hpp
@@ -29,7 +29,7 @@ namespace libtorrent
 	// we don't want these to clash with openssl's libcrypto
 	TORRENT_EXTRA_EXPORT void SHA1_init(sha1_ctx* context);
 	TORRENT_EXTRA_EXPORT void SHA1_update(sha1_ctx* context
-		, std::uint8_t const* data, std::uint32_t len);
+		, std::uint8_t const* data, size_t len);
 	TORRENT_EXTRA_EXPORT void SHA1_final(std::uint8_t* digest, sha1_ctx* context);
 }
 
diff --git a/include/libtorrent/sha512.hpp b/include/libtorrent/sha512.hpp
index b2449d833..f48056c0a 100644
--- a/include/libtorrent/sha512.hpp
+++ b/include/libtorrent/sha512.hpp
@@ -16,7 +16,7 @@ namespace libtorrent
 
 	TORRENT_EXTRA_EXPORT int SHA512_init(sha512_ctx* context);
 	TORRENT_EXTRA_EXPORT int SHA512_update(sha512_ctx* context
-		, std::uint8_t const* data, std::uint32_t len);
+		, std::uint8_t const* data, size_t len);
 	TORRENT_EXTRA_EXPORT int SHA512_final(std::uint8_t* digest, sha512_ctx* context);
 }
 
diff --git a/src/sha1.cpp b/src/sha1.cpp
index 87cec4a42..1f7705440 100644
--- a/src/sha1.cpp
+++ b/src/sha1.cpp
@@ -135,10 +135,10 @@ namespace
 #endif
 
 	template <class BlkFun>
-	void internal_update(sha1_ctx* context, u8 const* data, u32 len)
+	void internal_update(sha1_ctx* context, u8 const* data, size_t len)
 	{
 		using namespace std;
-		u32 i, j;	// JHB
+		size_t i, j;	// JHB
 
 #ifdef VERBOSE
 		SHAPrintContext(context, "before");
@@ -191,7 +191,7 @@ void SHA1_init(sha1_ctx* context)
 
 // Run your data through this.
 
-void SHA1_update(sha1_ctx* context, u8 const* data, u32 len)
+void SHA1_update(sha1_ctx* context, u8 const* data, size_t len)
 {
 	// GCC standard defines for endianness
 	// test with: cpp -dM /dev/null
diff --git a/src/sha512.cpp b/src/sha512.cpp
index 0f9d0913b..dc5b30ace 100644
--- a/src/sha512.cpp
+++ b/src/sha512.cpp
@@ -184,7 +184,7 @@ int SHA512_init(sha512_ctx* md) {
    @param inlen  The length of the data (octets)
    @return 0 if successful
 */
-int SHA512_update(sha512_ctx* md, std::uint8_t const* in, std::uint32_t inlen)
+int SHA512_update(sha512_ctx* md, std::uint8_t const* in, size_t inlen)
 {
     size_t n;
     size_t i;