diff --git a/tape/error.go b/tape/error.go
new file mode 100644
index 0000000..bf078ff
--- /dev/null
+++ b/tape/error.go
@@ -0,0 +1,11 @@
+package tape
+
+// Error enumerates common errors in this package.
+type Error string; const (
+	ErrTooLong Error = "data structure too long"
+)
+
+// Error implements the error interface.
+func (err Error) Error() string {
+	return string(err)
+}
diff --git a/tape/limits.go b/tape/limits.go
new file mode 100644
index 0000000..21fee47
--- /dev/null
+++ b/tape/limits.go
@@ -0,0 +1,13 @@
+package tape
+
+// MaxStructureLength determines how long a TAPE data structure can be. This
+// applies to:
+//
+//  - OTA
+//  - SBA/LBA
+//  - KTV
+//
+// By default it is set at 2^20 (about a million).
+// You shouldn't need to change this. If you do, it should only be set once at
+// the start of the program.
+var MaxStructureLength = 1024 * 1024