diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 8ab2dd526..637360e30 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -61,7 +61,7 @@
  * Maximum window size used for modular exponentiation. Default: 6
  * Minimum value: 1. Maximum value: 6.
  *
- * Result is an array of ( 2 << MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
+ * Result is an array of ( 2 ** MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
  * for the sliding window calculation. (So 64 by default)
  *
  * Reduction in size, reduces speed.