diff --git a/fox32os.def b/fox32os.def
index 73203f1..416bed3 100644
--- a/fox32os.def
+++ b/fox32os.def
@@ -12,6 +12,7 @@ yield_task:          jmp [0x00000A14]
 end_current_task:    jmp [0x00000A18]
 get_current_task_id: jmp [0x00000A1C]
 get_unused_task_id:  jmp [0x00000A20]
+is_task_id_used:     jmp [0x00000A24]
 
 ; memory jump table
 allocate_memory:     jmp [0x00000B10]
diff --git a/kernel/main.asm b/kernel/main.asm
index be8c166..8bb9503 100644
--- a/kernel/main.asm
+++ b/kernel/main.asm
@@ -28,6 +28,7 @@ jump_table:
     data.32 end_current_task
     data.32 get_current_task_id
     data.32 get_unused_task_id
+    data.32 is_task_id_used
 
     ; memory jump table
     org.pad 0x00000B10
diff --git a/kernel/task.asm b/kernel/task.asm
index 365be5f..7f16700 100644
--- a/kernel/task.asm
+++ b/kernel/task.asm
@@ -133,6 +133,15 @@ get_current_task_id:
     pop r2
     ret
 
+; check if a task ID is used
+; inputs:
+; r0: task ID
+; outputs:
+; Z flag: set if unused, reset if used
+is_task_id_used:
+    bts [task_id_bitmap], r0
+    ret
+
 task_load:
     mov r2, [r0] ; task ID
     add r0, 4