diff --git a/libguile/r6rs-ports.c b/libguile/r6rs-ports.c
index ffa1e1b2b..034564cfd 100644
--- a/libguile/r6rs-ports.c
+++ b/libguile/r6rs-ports.c
@@ -1,4 +1,4 @@
-/* Copyright 2009-2011,2013-2015,2018-2019,2023,2024
+/* Copyright 2009-2011,2013-2015,2018-2019,2023,2024,2025
      Free Software Foundation, Inc.
 
    This file is part of Guile.
@@ -515,6 +515,26 @@ SCM_DEFINE (scm_unget_bytevector, "unget-bytevector", 2, 2, 0,
 #undef FUNC_NAME
 
 
+
+
+
+static void*
+grow_byte_buffer (void *p, size_t old_size, size_t new_size)
+{
+  void *new_p = scm_gc_malloc_pointerless (new_size, NULL);
+  memcpy (new_p, p, old_size);
+  return new_p;
+}
+
+static void*
+shrink_byte_buffer (void *p, size_t old_size, size_t new_size)
+{
+  void *new_p = scm_gc_malloc_pointerless (new_size, NULL);
+  memcpy (new_p, p, new_size);
+  return new_p;
+}
+
+
 
 
 /* Bytevector output port.  */
@@ -581,8 +601,7 @@ bytevector_output_port_buffer_grow (scm_t_bytevector_output_port_buffer *buf,
       if (INT_ADD_OVERFLOW (buf->total_len, buf->total_len))
         scm_num_overflow ("bytevector_output_port_buffer_grow");
       new_size = MAX (min_size, buf->total_len * 2);
-      new_buf = scm_gc_realloc ((void *) buf->buffer, buf->total_len,
-                                new_size, SCM_GC_BYTEVECTOR_OUTPUT_PORT);
+      new_buf = grow_byte_buffer (buf->buffer, buf->total_len, new_size);
     }
   else
     {
@@ -696,10 +715,9 @@ SCM_SMOB_APPLY (bytevector_output_port_procedure,
     {
       if (result_buf.total_len > result_buf.len)
 	/* Shrink the buffer.  */
-	result_buf.buffer = scm_gc_realloc ((void *) result_buf.buffer,
-					    result_buf.total_len,
-					    result_buf.len,
-					    SCM_GC_BYTEVECTOR_OUTPUT_PORT);
+	result_buf.buffer = shrink_byte_buffer (result_buf.buffer,
+                                                result_buf.total_len,
+                                                result_buf.len);
 
       bv = scm_c_take_gc_bytevector ((signed char *) result_buf.buffer,
                                      result_buf.len, SCM_BOOL_F);