diff --git a/kitty/simd-string.c b/kitty/simd-string.c
index 1ed54d9ec..e8cef9e5d 100644
--- a/kitty/simd-string.c
+++ b/kitty/simd-string.c
@@ -124,6 +124,35 @@ find_either_of_two_bytes_sse4_2(uint8_t *haystack, const size_t sz, const uint8_
     return ans;
 }
 
+static uint8_t*
+find_either_of_two_bytes_avx2(uint8_t *haystack, size_t sz, const uint8_t a, const uint8_t b) {
+    const size_t extra = (uintptr_t)haystack % sizeof(__m256i);
+    if (extra) { // need aligned loads for performance so search first few bytes by hand
+        size_t es = MIN(sz, sizeof(__m256i) - extra);
+        uint8_t *ans = (has_sse4_2 && es > 15) ? find_either_of_two_bytes_sse4_2(haystack, es, a, b) : find_either_of_two_bytes_simple(haystack, es, a, b);
+        if (ans) return ans;
+        sz -= es;
+        haystack += es;
+        if (!sz) return NULL;
+    }
+    __m256i x = _mm256_set1_epi8(a);
+    __m256i y = _mm256_set1_epi8(b);
+    for (const uint8_t* limit = haystack + sz; haystack < limit; haystack += sizeof(__m256i)) {
+        __m256i chunk = _mm256_load_si256((__m256i*)(haystack));
+        __m256i x_cmp = _mm256_cmpeq_epi8(chunk, x);
+        __m256i y_cmp = _mm256_cmpeq_epi8(chunk, y);
+        __m256i matches = _mm256_or_si256(x_cmp, y_cmp);
+        const int mask = _mm256_movemask_epi8(matches);
+        if (mask != 0) {
+            // The trailing zeroes in mask give us the position of the first match
+            size_t pos = __builtin_ctz(mask);
+            if (haystack + pos < limit) return haystack + pos;
+        }
+    }
+    return NULL;
+}
+
+
 static uint8_t* (*find_either_of_two_bytes_impl)(uint8_t*, const size_t, const uint8_t, const uint8_t) = find_either_of_two_bytes_simple;
 
 uint8_t*
@@ -195,10 +224,10 @@ find_byte_not_in_range_avx2(uint8_t *haystack, size_t sz, const uint8_t a, const
         __m256i above_lower = _mm256_cmpgt_epi8(chunk, lower_bound);
         __m256i below_upper = _mm256_cmpgt_epi8(upper_bound, chunk);
         __m256i in_range = _mm256_and_si256(above_lower, below_upper);
-        int mask = _mm256_movemask_epi8(in_range);
-        if (mask != (int)0xFFFFFFFF) {
-            // The trailing zeroes in ~mask give us the position
-            const size_t pos = __builtin_ctz(~mask);
+        const int mask = ~_mm256_movemask_epi8(in_range); // ~ as we want not in range
+        if (mask != 0) {
+            // The trailing zeroes in mask give us the position of the first match on little endian
+            const int pos = __builtin_ctz(mask);
             if (haystack + pos < limit) return haystack + pos;
         }
     }
@@ -221,13 +250,14 @@ init_simd(void *x) {
     if (has_avx2) {
         A(has_avx2, True);
         find_byte_not_in_range_impl = find_byte_not_in_range_avx2;
+        find_either_of_two_bytes_impl = find_either_of_two_bytes_avx2;
     } else {
         A(has_avx2, False);
     }
     if (has_sse4_2) {
         A(has_sse4_2, True);
         if (find_byte_not_in_range == find_byte_not_in_range_simple) find_byte_not_in_range_impl = find_byte_not_in_range_sse4_2;
-        find_either_of_two_bytes_impl = find_either_of_two_bytes_sse4_2;
+        if (find_either_of_two_bytes_impl == find_either_of_two_bytes_simple) find_either_of_two_bytes_impl = find_either_of_two_bytes_sse4_2;
     } else {
         A(has_sse4_2, False);
     }