diff --git a/libsrc/rp6502/read.c b/libsrc/rp6502/read.c
index eb96f779c..87a9bbf7d 100644
--- a/libsrc/rp6502/read.c
+++ b/libsrc/rp6502/read.c
@@ -5,7 +5,7 @@ int __fastcall__ read (int fildes, void* buf, unsigned count)
 {
     int total = 0;
     while (count) {
-        unsigned blockcount = (count > 256) ? 256 : count;
+        unsigned blockcount = (count > 512) ? 512 : count;
         int bytes_read = read_xstack (&((char*)buf)[total], blockcount, fildes);
         if (bytes_read < 0) {
             return bytes_read;
diff --git a/libsrc/rp6502/sysrename.c b/libsrc/rp6502/sysrename.c
index 96eca24cf..46bdd8b31 100644
--- a/libsrc/rp6502/sysrename.c
+++ b/libsrc/rp6502/sysrename.c
@@ -7,7 +7,7 @@ unsigned char __fastcall__ _sysrename (const char* oldpath, const char* newpath)
     size_t oldpathlen, newpathlen;
     oldpathlen = strlen (oldpath);
     newpathlen = strlen (newpath);
-    if (oldpathlen + newpathlen > 254) {
+    if (oldpathlen + newpathlen > 510) {
         return _mappederrno (EINVAL);
     }
     while (oldpathlen) {
diff --git a/libsrc/rp6502/write.c b/libsrc/rp6502/write.c
index 11241dab5..23877b6e8 100644
--- a/libsrc/rp6502/write.c
+++ b/libsrc/rp6502/write.c
@@ -5,7 +5,7 @@ int __fastcall__ write (int fildes, const void* buf, unsigned count)
 {
     int ax, total = 0;
     while (count) {
-        int blockcount = (count > 256) ? 256 : count;
+        int blockcount = (count > 512) ? 512 : count;
         ax = write_xstack (&((char*)buf)[total], blockcount, fildes);
         if (ax < 0) {
             return ax;
diff --git a/libsrc/rp6502/write_xstack.c b/libsrc/rp6502/write_xstack.c
index ff979899d..29285a87e 100644
--- a/libsrc/rp6502/write_xstack.c
+++ b/libsrc/rp6502/write_xstack.c
@@ -4,7 +4,7 @@
 int __fastcall__ write_xstack (const void* buf, unsigned count, int fildes)
 {
     unsigned i;
-    if (count > 256) {
+    if (count > 512) {
         return _mappederrno (EINVAL);
     }
     for (i = count; i;) {