diff --git a/src/slave.c b/src/slave.c
index 9da41ac2..0af89d52 100644
--- a/src/slave.c
+++ b/src/slave.c
@@ -176,7 +176,7 @@ static client_t *open_relay_connection (relay_server *relay)
 
         auth_header = malloc (len);
         snprintf (auth_header, len, "%s:%s", relay->username, relay->password);
-        esc_authorisation = util_base64_encode(auth_header);
+        esc_authorisation = util_base64_encode(auth_header, len);
         free(auth_header);
         len = strlen (esc_authorisation) + 24;
         auth_header = malloc (len);
@@ -637,7 +637,7 @@ static int update_from_master(ice_config_t *config)
         len = strlen(username) + strlen(password) + 2;
         authheader = malloc(len);
         snprintf (authheader, len, "%s:%s", username, password);
-        data = util_base64_encode(authheader);
+        data = util_base64_encode(authheader, len);
         sock_write (mastersock,
                 "GET /admin/streamlist.txt HTTP/1.0\r\n"
                 "Authorization: Basic %s\r\n"
diff --git a/src/util.c b/src/util.c
index 5eaed9c7..f26669b9 100644
--- a/src/util.c
+++ b/src/util.c
@@ -409,15 +409,13 @@ char *util_bin_to_hex(unsigned char *data, int len)
 }
 
 /* This isn't efficient, but it doesn't need to be */
-char *util_base64_encode(const char *data)
-{
-    int len = strlen(data);
+char *util_base64_encode(const char *data, size_t len) {
     char *out = malloc(len*4/3 + 4);
     char *result = out;
-    int chunk;
+    size_t chunk;
 
     while(len > 0) {
-        chunk = (len >3)?3:len;
+        chunk = len > 3 ? 3 : len;
         *out++ = base64table[(*data & 0xFC)>>2];
         *out++ = base64table[((*data & 0x03)<<4) | ((*(data+1) & 0xF0) >> 4)];
         switch(chunk) {
diff --git a/src/util.h b/src/util.h
index f735246c..e31353f2 100644
--- a/src/util.h
+++ b/src/util.h
@@ -32,7 +32,7 @@ char *util_get_extension(const char *path);
 char *util_get_path_from_uri(char *uri);
 char *util_get_path_from_normalised_uri(const char *uri);
 char *util_normalise_uri(const char *uri);
-char *util_base64_encode(const char *data);
+char *util_base64_encode(const char *data, size_t len);
 char *util_base64_decode(const char *input);
 char *util_bin_to_hex(unsigned char *data, int len);