diff --git a/src/internal.c b/src/internal.c
index 913dc1335..6d531b621 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -7831,7 +7831,7 @@ static int DoHandShakeMsg(WOLFSSL* ssl, byte* input, word32* inOutIdx,
 
 static INLINE int DtlsCheckWindow(WOLFSSL* ssl)
 {
-    DtlsSeq window;
+    word32* window;
     word16 cur_hi, next_hi;
     word32 cur_lo, next_lo, diff;
     int curLT;
@@ -7869,23 +7869,28 @@ static INLINE int DtlsCheckWindow(WOLFSSL* ssl)
     }
 
     /* Check to see that the next value is greater than the number of messages
-     * trackable in the window (32 or 64), and that the difference between the
-     * next expected sequence number and the received sequence number is
-     * inside the window. */
+     * trackable in the window, and that the difference between the next
+     * expected sequence number and the received sequence number is inside the
+     * window. */
     if ((next_hi || next_lo > DTLS_SEQ_BITS) &&
         curLT && (diff > DTLS_SEQ_BITS)) {
 
         WOLFSSL_MSG("Current record sequence number from the past.");
         return 0;
     }
-    else if (curLT && (window & ((DtlsSeq)1 << (diff - 1)))) {
-        WOLFSSL_MSG("Current record sequence number already received.");
-        return 0;
-    }
     else if (!curLT && (diff > DTLS_SEQ_BITS)) {
         WOLFSSL_MSG("Rejecting message too far into the future.");
         return 0;
     }
+    else if (curLT) {
+        word32 idx = diff / DTLS_WORD_BITS;
+        word32 newDiff = diff % DTLS_WORD_BITS;
+
+        if (window[idx] & (1 << (newDiff - 1))) {
+            WOLFSSL_MSG("Current record sequence number already received.");
+            return 0;
+        }
+    }
 
     return 1;
 }
@@ -7893,7 +7898,7 @@ static INLINE int DtlsCheckWindow(WOLFSSL* ssl)
 
 static INLINE int DtlsUpdateWindow(WOLFSSL* ssl)
 {
-    DtlsSeq* window;
+    word32* window;
     word32* next_lo;
     word16* next_hi;
     int curLT;
@@ -7903,12 +7908,12 @@ static INLINE int DtlsUpdateWindow(WOLFSSL* ssl)
     if (ssl->keys.curEpoch == ssl->keys.nextEpoch) {
         next_hi = &ssl->keys.nextSeq_hi;
         next_lo = &ssl->keys.nextSeq_lo;
-        window = &ssl->keys.window;
+        window = ssl->keys.window;
     }
     else {
         next_hi = &ssl->keys.prevSeq_hi;
         next_lo = &ssl->keys.prevSeq_lo;
-        window = &ssl->keys.prevWindow;
+        window = ssl->keys.prevWindow;
     }
 
     cur_hi = ssl->keys.curSeq_hi;
@@ -7924,14 +7929,36 @@ static INLINE int DtlsUpdateWindow(WOLFSSL* ssl)
     }
 
     if (curLT) {
-        *window |= ((DtlsSeq)1 << (diff - 1));
+        word32 idx = diff / DTLS_WORD_BITS;
+        word32 newDiff = diff % DTLS_WORD_BITS;
+
+        window[idx] |= (1 << (newDiff - 1));
     }
     else {
         if (diff >= DTLS_SEQ_BITS)
-            *window = 0;
-        else
-            *window <<= (1 + diff);
-        *window |= 1;
+            XMEMSET(window, 0, DTLS_SEQ_SZ);
+        else {
+            word32 idx, newDiff, temp, i;
+            word32 oldWindow[WOLFSSL_DTLS_WINDOW_WORDS];
+
+            temp = 0;
+            diff++;
+            idx = diff / DTLS_WORD_BITS;
+            newDiff = diff % DTLS_WORD_BITS;
+
+            XMEMCPY(oldWindow, window, sizeof(oldWindow));
+
+            for (i = 0; i < WOLFSSL_DTLS_WINDOW_WORDS; i++) {
+                if (i < idx)
+                    window[i] = 0;
+                else {
+                    temp |= (oldWindow[i-idx] << newDiff);
+                    window[i] = temp;
+                    temp = oldWindow[i-idx] >> (DTLS_WORD_BITS - newDiff);
+                }
+            }
+        }
+        window[0] |= 1;
         *next_lo = cur_lo + 1;
         if (*next_lo < cur_lo)
             (*next_hi)++;
@@ -9597,8 +9624,9 @@ int ProcessReply(WOLFSSL* ssl)
                             DtlsMsgPoolReset(ssl);
                             ssl->keys.nextEpoch++;
                             ssl->keys.nextSeq_lo = 0;
-                            ssl->keys.prevWindow = ssl->keys.window;
-                            ssl->keys.window = 0;
+                            XMEMCPY(ssl->keys.prevWindow, ssl->keys.window,
+                                    DTLS_SEQ_SZ);
+                            XMEMSET(ssl->keys.window, 0, DTLS_SEQ_SZ);
                         }
                     #endif
 
diff --git a/wolfssl/internal.h b/wolfssl/internal.h
index b29199fae..3f895df1f 100644
--- a/wolfssl/internal.h
+++ b/wolfssl/internal.h
@@ -1584,12 +1584,13 @@ typedef struct WOLFSSL_DTLS_CTX {
 
 #ifdef WOLFSSL_DTLS
 
-    #ifdef WORD64_AVAILABLE
-        typedef word64 DtlsSeq;
-    #else
-        typedef word32 DtlsSeq;
-    #endif
-    #define DTLS_SEQ_BITS (sizeof(DtlsSeq) * CHAR_BIT)
+    #ifndef WOLFSSL_DTLS_WINDOW_WORDS
+        #define WOLFSSL_DTLS_WINDOW_WORDS 2
+    #endif /* WOLFSSL_DTLS_WINDOW_WORDS */
+
+    #define DTLS_WORD_BITS (sizeof(word32) * CHAR_BIT)
+    #define DTLS_SEQ_BITS  (WOLFSSL_DTLS_WINDOW_WORDS * DTLS_WORD_BITS)
+    #define DTLS_SEQ_SZ    (sizeof(word32) * WOLFSSL_DTLS_WINDOW_WORDS)
 
 #endif /* WOLFSSL_DTLS */
 
@@ -1617,7 +1618,8 @@ typedef struct Keys {
     word32 sequence_number_lo;
 
 #ifdef WOLFSSL_DTLS
-    DtlsSeq window;     /* Sliding window for current epoch    */
+    word32 window[WOLFSSL_DTLS_WINDOW_WORDS];
+                        /* Sliding window for current epoch    */
     word16 nextEpoch;   /* Expected epoch in next record       */
     word16 nextSeq_hi;  /* Expected sequence in next record    */
     word32 nextSeq_lo;
@@ -1626,7 +1628,8 @@ typedef struct Keys {
     word16 curSeq_hi;   /* Received sequence in current record */
     word32 curSeq_lo;
 
-    DtlsSeq prevWindow; /* Sliding window for old epoch        */
+    word32 prevWindow[WOLFSSL_DTLS_WINDOW_WORDS];
+                        /* Sliding window for old epoch        */
     word16 prevSeq_hi;  /* Next sequence in allowed old epoch  */
     word32 prevSeq_lo;