diff -r 02a56701a5cb -r 7df0bcaecffa src/string.c
--- a/src/string.c	Tue Oct 04 18:55:20 2022 +0200
+++ b/src/string.c	Tue Oct 04 19:25:07 2022 +0200
@@ -227,14 +227,7 @@
     return (cxmutstr) {(char *) result.ptr, result.length};
 }
 
-#define ptable_r(dest, useheap, ptable, index) (dest = useheap ? \
-    ((size_t*)ptable)[index] : (size_t) ((uint8_t*)ptable)[index])
-
-#define ptable_w(useheap, ptable, index, src) do {\
-    if (!useheap) ((uint8_t*)ptable)[index] = (uint8_t) src;\
-    else ((size_t*)ptable)[index] = src;\
-    } while (0)
-
+#define STRSTR_SBO_BUFLEN 512
 
 cxstring cx_strstr(
         cxstring haystack,
@@ -257,14 +250,14 @@
      * and we want to avoid that.
      */
 
-    /* static prefix table */
-    static uint8_t s_prefix_table[512];
+    /* local prefix table */
+    size_t s_prefix_table[STRSTR_SBO_BUFLEN];
 
-    /* check pattern length and use appropriate prefix table */
+    /* check needle length and use appropriate prefix table */
     /* if the pattern exceeds static prefix table, allocate on the heap */
-    register int useheap = needle.length >= 512;
-    register void *ptable = useheap ? calloc(needle.length + 1,
-                                             sizeof(size_t)) : s_prefix_table;
+    bool useheap = needle.length >= STRSTR_SBO_BUFLEN;
+    register size_t *ptable = useheap ? calloc(needle.length + 1,
+                                               sizeof(size_t)) : s_prefix_table;
 
     /* keep counter in registers */
     register size_t i, j;
@@ -272,14 +265,14 @@
     /* fill prefix table */
     i = 0;
     j = 0;
-    ptable_w(useheap, ptable, i, j);
+    ptable[i] = j;
     while (i < needle.length) {
         while (j >= 1 && needle.ptr[j - 1] != needle.ptr[i]) {
-            ptable_r(j, useheap, ptable, j - 1);
+            j = ptable[j - 1];
         }
         i++;
         j++;
-        ptable_w(useheap, ptable, i, j);
+        ptable[i] = j;
     }
 
     /* search */
@@ -288,7 +281,7 @@
     j = 1;
     while (i < haystack.length) {
         while (j >= 1 && haystack.ptr[i] != needle.ptr[j - 1]) {
-            ptable_r(j, useheap, ptable, j - 1);
+            j = ptable[j - 1];
         }
         i++;
         j++;