diff --git a/src/lib/lwan-websocket.c b/src/lib/lwan-websocket.c
index ab4f4253c..b83c6950f 100644
--- a/src/lib/lwan-websocket.c
+++ b/src/lib/lwan-websocket.c
@@ -150,44 +150,40 @@ static size_t get_frame_length(struct lwan_request *request, uint16_t header)
 
 static void unmask(char *msg, size_t msg_len, char mask[static 4])
 {
-    const uint32_t mask32 = string_as_uint32(mask);
-    char *msg_end = msg + msg_len;
-
-    if (sizeof(void *) == 8) {
-        const uint64_t mask64 = (uint64_t)mask32 << 32 | mask32;
+    const int32_t mask32 = (int32_t)string_as_uint32(mask);
+    const char *msg_end = msg + msg_len;
 
 #if defined(__AVX2__)
-        const size_t len256 = msg_len / 32;
-        if (len256) {
-            const __m256i mask256 =
-                _mm256_setr_epi64x((int64_t)mask64, (int64_t)mask64,
-                                   (int64_t)mask64, (int64_t)mask64);
-            for (size_t i = 0; i < len256; i++) {
-                __m256i v = _mm256_loadu_si256((__m256i *)msg);
-                _mm256_storeu_si256((__m256i *)msg,
-                                    _mm256_xor_si256(v, mask256));
-                msg += 32;
-            }
-
-            msg_len = (size_t)(msg_end - msg);
+    const size_t len256 = msg_len / 32;
+    if (len256) {
+        const __m256i mask256 = _mm256_setr_epi32(
+            mask32, mask32, mask32, mask32, mask32, mask32, mask32, mask32);
+        for (size_t i = 0; i < len256; i++) {
+            __m256i v = _mm256_loadu_si256((__m256i *)msg);
+            _mm256_storeu_si256((__m256i *)msg, _mm256_xor_si256(v, mask256));
+            msg += 32;
         }
+
+        msg_len = (size_t)(msg_end - msg);
+    }
 #endif
 
 #if defined(__SSE2__)
-        const size_t len128 = msg_len / 16;
-        if (len128) {
-            const __m128i mask128 =
-                _mm_setr_epi64((__m64)mask64, (__m64)mask64);
-            for (size_t i = 0; i < len128; i++) {
-                __m128i v = _mm_loadu_si128((__m128i *)msg);
-                _mm_storeu_si128((__m128i *)msg, _mm_xor_si128(v, mask128));
-                msg += 16;
-            }
-
-            msg_len = (size_t)(msg_end - msg);
+    const size_t len128 = msg_len / 16;
+    if (len128) {
+        const __m128i mask128 = _mm_setr_epi32(mask32, mask32, mask32, mask32);
+        for (size_t i = 0; i < len128; i++) {
+            __m128i v = _mm_loadu_si128((__m128i *)msg);
+            _mm_storeu_si128((__m128i *)msg, _mm_xor_si128(v, mask128));
+            msg += 16;
         }
+
+        msg_len = (size_t)(msg_end - msg);
+    }
 #endif
 
+    if (sizeof(void *) == 8) {
+        const uint64_t mask64 = (uint64_t)mask32 << 32 | (uint64_t)mask32;
         const size_t len64 = msg_len / 8;
         for (size_t i = 0; i < len64; i++) {
             uint64_t v = string_as_uint64(msg);
@@ -199,7 +195,7 @@ static void unmask(char *msg, size_t msg_len, char mask[static 4])
     const size_t len32 = (size_t)((msg_end - msg) / 4);
     for (size_t i = 0; i < len32; i++) {
         uint32_t v = string_as_uint32(msg);
-        v ^= mask32;
+        v ^= (uint32_t)mask32;
         msg = mempcpy(msg, &v, sizeof(v));
     }