diff --git a/ChangeLog.d/adjusting sliding_window_size_PR3592.txt b/ChangeLog.d/adjusting sliding_window_size_PR3592.txt
new file mode 100644
index 0000000000..6089565413
--- /dev/null
+++ b/ChangeLog.d/adjusting sliding_window_size_PR3592.txt	
@@ -0,0 +1,3 @@
+Changes
+   * Reduce stack usage significantly during sliding window exponentiation.
+     Reported in #3591 and fix contributed in #3592 by Daniel Otte.
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 754b50a3bf..a2fa3bdaf7 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -83,12 +83,12 @@
  * 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.
  */
-#define MBEDTLS_MPI_WINDOW_SIZE                           6        /**< Maximum windows size used. */
+#define MBEDTLS_MPI_WINDOW_SIZE                           6        /**< Maximum window size used. */
 #endif /* !MBEDTLS_MPI_WINDOW_SIZE */
 
 #if !defined(MBEDTLS_MPI_MAX_SIZE)
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index d8332dae5a..d23a7efcc1 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -2814,7 +2814,7 @@
  */
 
 /* MPI / BIGNUM options */
-//#define MBEDTLS_MPI_WINDOW_SIZE            6 /**< Maximum windows size used. */
+//#define MBEDTLS_MPI_WINDOW_SIZE            6 /**< Maximum window size used. */
 //#define MBEDTLS_MPI_MAX_SIZE            1024 /**< Maximum number of bytes for usable MPIs. */
 
 /* CTR_DRBG options */
diff --git a/library/bignum.c b/library/bignum.c
index 3135ec4adc..0e39e3a443 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1850,7 +1850,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
     size_t i, j, nblimbs;
     size_t bufsize, nbits;
     mbedtls_mpi_uint ei, mm, state;
-    mbedtls_mpi RR, T, W[ 2 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
+    mbedtls_mpi RR, T, W[ 1 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
     int neg;
 
     if( mbedtls_mpi_cmp_int( N, 0 ) <= 0 || ( N->p[0] & 1 ) == 0 )