diff --git a/day4.c b/day4.c
index 5a2f23a..10b8fa8 100644
--- a/day4.c
+++ b/day4.c
@@ -12,7 +12,7 @@ unsigned char test[] = {
 #embed "day4_test.txt"
 };
 
-static
+alignas (0x40) static
 unsigned char buf[UINT16_MAX];
 
 static
@@ -31,9 +31,9 @@ unsigned long do_part1(size_t file_len, unsigned char file[file_len]) {
 
     unsigned line_count = file_len / file_stride;
 
-    unsigned line_stride = file_stride + 1;
+    unsigned line_stride = MAX(file_stride + 1, 0x40);
 
-    memset(d, '0', sizeof(buf));
+    memset(d, 0, sizeof(buf));
 
 #if DBG
     printh(file_stride); print("\n");
@@ -59,7 +59,7 @@ unsigned long do_part1(size_t file_len, unsigned char file[file_len]) {
     unsigned char *l = buf + line_stride + 1;
     for (unsigned i = line_count; i; i--) {
         d = l;
-        for (unsigned j = line_stride - 2; j; j--) {
+        for (unsigned j = file_stride - 1; j; j--) {
             if (*d == '@') {
                 unsigned neighbors = 0
                     + (*(d - 1 - line_stride) == '@')
@@ -69,9 +69,18 @@ unsigned long do_part1(size_t file_len, unsigned char file[file_len]) {
                     + (*(d + 1 - 0) == '@')
                     + (*(d - 1 + line_stride) == '@')
                     + (*(d - 0 + line_stride) == '@')
-                    + (*(d + 1 + line_stride) == '@');
+                    + (*(d + 1 + line_stride) == '@')
+                    + (*(d - 1 - line_stride) == 'X')
+                    + (*(d - 0 - line_stride) == 'X')
+                    + (*(d + 1 - line_stride) == 'X')
+                    + (*(d - 1 - 0) == 'X')
+                    + (*(d + 1 - 0) == 'X')
+                    + (*(d - 1 + line_stride) == 'X')
+                    + (*(d - 0 + line_stride) == 'X')
+                    + (*(d + 1 + line_stride) == 'X');
                 if (neighbors < 4) {
                     result++;
+                    *d = 'X';
                 }
             }
             d++;
@@ -98,9 +107,9 @@ unsigned long do_part2(size_t file_len, unsigned char file[file_len]) {
 
     unsigned line_count = file_len / file_stride;
 
-    unsigned line_stride = file_stride + 1;
+    unsigned line_stride = MAX(file_stride + 1, 0x40);
 
-    memset(d, '0', sizeof(buf));
+    memset(d, 0, sizeof(buf));
 
 #if DBG
     printh(file_stride); print("\n");
@@ -127,7 +136,7 @@ unsigned long do_part2(size_t file_len, unsigned char file[file_len]) {
     for (unsigned i = line_count; i; i--) {
 line_start:
         d = l;
-        for (unsigned j = line_stride - 2; j; j--) {
+        for (unsigned j = file_stride - 1; j; j--) {
             if (*d == '@') {
                 unsigned neighbors = 0
                     + (*(d - 1 - line_stride) == '@')
@@ -161,9 +170,9 @@ line_start:
 }
 
 #define RUN_TEST1 1
-#define RUN_PART1 1
+#define RUN_PART1 0
 #define RUN_TEST2 1
-#define RUN_PART2 1
+#define RUN_PART2 0
 
 #define TEST1_EXPECT 13
 #define TEST2_EXPECT 43