diff --git a/lib/syslib/vm_allocmem.c b/lib/syslib/vm_allocmem.c
index 725ac54ce..a277fcf7d 100644
--- a/lib/syslib/vm_allocmem.c
+++ b/lib/syslib/vm_allocmem.c
@@ -11,7 +11,7 @@ PUBLIC int vm_allocmem(phys_clicks bytes, phys_clicks *retmembase)
     message m;
     int result;
 
-    m.VMAM_BYTES = bytes;
+    m.VMAM_BYTES = (char *) bytes;
     result = _taskcall(VM_PROC_NR, VM_ALLOCMEM, &m);
     if(result == OK)
 	    *retmembase = m.VMAM_MEMBASE;