diff --git a/tsdb/index/index.go b/tsdb/index/index.go
index 1ddcac9501..8a76770821 100644
--- a/tsdb/index/index.go
+++ b/tsdb/index/index.go
@@ -17,6 +17,7 @@ import (
 	"bufio"
 	"context"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"hash"
 	"hash/crc32"
@@ -94,6 +95,13 @@ func (s indexWriterStage) String() string {
 	return "<unknown>"
 }
 
+// ErrPostingsOffsetTableTooLarge is returned when the postings offset table length
+// would exceed 4 bytes (table would exceed the 4GB limit).
+var ErrPostingsOffsetTableTooLarge = errors.New("length size exceeds 4 bytes")
+
+// ErrIndexExceeds64GiB is returned when the index file would exceed the 64GiB limit.
+var ErrIndexExceeds64GiB = errors.New("exceeding max size of 64GiB")
+
 // The table gets initialized with sync.Once but may still cause a race
 // with any other use of the crc32 package anywhere. Thus we initialize it
 // before.
@@ -303,7 +311,7 @@ func (fw *FileWriter) Write(bufs ...[]byte) error {
 		// Once we move to compressed/varint representations in those areas, this limitation
 		// can be lifted.
 		if fw.pos > 16*math.MaxUint32 {
-			return fmt.Errorf("%q exceeding max size of 64GiB", fw.name)
+			return fmt.Errorf("%q %w", fw.name, ErrIndexExceeds64GiB)
 		}
 	}
 	return nil
@@ -660,7 +668,7 @@ func (w *Writer) writeLengthAndHash(startPos uint64) error {
 	w.buf1.Reset()
 	l := w.f.pos - startPos - 4
 	if l > math.MaxUint32 {
-		return fmt.Errorf("length size exceeds 4 bytes: %d", l)
+		return fmt.Errorf("%w: %d", ErrPostingsOffsetTableTooLarge, l)
 	}
 	w.buf1.PutBE32int(int(l))
 	if err := w.writeAt(w.buf1.Get(), startPos); err != nil {