diff --git a/bsd-user/bsd-ioctl.c b/bsd-user/bsd-ioctl.c
index 3940a69260..15e80bb21e 100644
--- a/bsd-user/bsd-ioctl.c
+++ b/bsd-user/bsd-ioctl.c
@@ -392,3 +392,45 @@ abi_long do_bsd_ioctl(int fd, abi_long cmd, abi_long arg)
     }
     return ret;
 }
+
+void init_bsd_ioctl(void)
+{
+    IOCTLEntry *ie;
+    const argtype *arg_type;
+    int size;
+
+    thunk_init(STRUCT_MAX);
+
+#define STRUCT(name, ...) \
+ thunk_register_struct(STRUCT_ ## name, #name, struct_ ## name ## _def);
+#define STRUCT_SPECIAL(name) \
+ thunk_register_struct_direct(STRUCT_ ## name, #name, &struct_ ## name ## _def);
+#include "os-ioctl-types.h"
+#undef STRUCT
+#undef STRUCT_SPECIAL
+
+    /*
+     * Patch the ioctl size if necessary using the fact that no
+     * ioctl has all the bits at '1' in the size field
+     * (IOCPARM_MAX - 1).
+     */
+    ie = ioctl_entries;
+    while (ie->target_cmd != 0) {
+        if (((ie->target_cmd >> TARGET_IOCPARM_SHIFT) &
+                    TARGET_IOCPARM_MASK) == TARGET_IOCPARM_MASK) {
+            arg_type = ie->arg_type;
+            if (arg_type[0] != TYPE_PTR) {
+                fprintf(stderr, "cannot patch size for ioctl 0x%x\n",
+                        ie->target_cmd);
+                exit(1);
+            }
+            arg_type++;
+            size = thunk_type_size(arg_type, 0);
+            ie->target_cmd = (ie->target_cmd &
+                    ~(TARGET_IOCPARM_MASK << TARGET_IOCPARM_SHIFT)) |
+                (size << TARGET_IOCPARM_SHIFT);
+        }
+        ie++;
+    }
+
+}