diff --git a/src/add-ons/kernel/file_systems/bfs/BlockAllocator.cpp b/src/add-ons/kernel/file_systems/bfs/BlockAllocator.cpp
index cf13c1bd49..5a6c642910 100644
--- a/src/add-ons/kernel/file_systems/bfs/BlockAllocator.cpp
+++ b/src/add-ons/kernel/file_systems/bfs/BlockAllocator.cpp
@@ -642,10 +642,23 @@ BlockAllocator::Free(Transaction *transaction, block_run run)
 //	the "chkbfs" command
 
 
+bool 
+BlockAllocator::IsValidCheckControl(check_control *control)
+{
+	if (control == NULL
+		|| control->magic != BFS_IOCTL_CHECK_MAGIC) {
+		FATAL(("invalid check_control (%p)!\n", control));
+		return false;
+	}
+
+	return true;
+}
+
+
 status_t 
 BlockAllocator::StartChecking(check_control *control)
 {
-	if (control == NULL)
+	if (!IsValidCheckControl(control))
 		return B_BAD_VALUE;
 
 	status_t status = fLock.Lock();
@@ -771,7 +784,7 @@ BlockAllocator::StopChecking(check_control *control)
 status_t
 BlockAllocator::CheckNextNode(check_control *control)
 {
-	if (control == NULL)
+	if (!IsValidCheckControl(control))
 		return B_BAD_VALUE;
 
 	check_cookie *cookie = (check_cookie *)control->cookie;
diff --git a/src/add-ons/kernel/file_systems/bfs/BlockAllocator.h b/src/add-ons/kernel/file_systems/bfs/BlockAllocator.h
index ffd47d50b5..e023a5f83a 100644
--- a/src/add-ons/kernel/file_systems/bfs/BlockAllocator.h
+++ b/src/add-ons/kernel/file_systems/bfs/BlockAllocator.h
@@ -44,6 +44,7 @@ class BlockAllocator {
 		status_t CheckInode(Inode *inode, check_control *control = NULL);
 
 	private:
+		bool IsValidCheckControl(check_control *control);
 		bool CheckBitmapIsUsedAt(off_t block) const;
 		void SetCheckBitmapAt(off_t block);
 
diff --git a/src/add-ons/kernel/file_systems/bfs/bfs_control.h b/src/add-ons/kernel/file_systems/bfs/bfs_control.h
index b4a9da8574..858aa54a0f 100644
--- a/src/add-ons/kernel/file_systems/bfs/bfs_control.h
+++ b/src/add-ons/kernel/file_systems/bfs/bfs_control.h
@@ -34,6 +34,7 @@ extern "C" {
  * BFS_IOCTL_START_CHECKING is called
  */
 struct check_control {
+	uint32		magic;
 	uint32		flags;
 	char		name[B_FILE_NAME_LENGTH];
 	vnode_id	inode;
@@ -69,4 +70,7 @@ struct check_control {
 #define BFS_WRONG_TYPE			16
 #define BFS_NAMES_DONT_MATCH	32
 
+/* check control magic value */
+#define BFS_IOCTL_CHECK_MAGIC	'BChk'
+
 #endif	/* BFS_CONTROL_H */