diff --git a/include/cmplog.h b/include/cmplog.h
index e4821444..5601beef 100644
--- a/include/cmplog.h
+++ b/include/cmplog.h
@@ -59,14 +59,15 @@ struct cmp_operands {
   u64 v1;
   u64 v0_128;
   u64 v1_128;
+  u64 unused;
 
 } __attribute__((packed));
 
 struct cmpfn_operands {
 
-  u8 v0[31];
+  u8 v0[31 + _CMPLOG_EXTRA];
   u8 v0_len;
-  u8 v1[31];
+  u8 v1[31 + _CMPLOG_EXTRA];
   u8 v1_len;
 
 } __attribute__((packed));
diff --git a/include/config.h b/include/config.h
index 988e536e..1f9902d4 100644
--- a/include/config.h
+++ b/include/config.h
@@ -60,6 +60,9 @@
  *
  */
 
+/* Support 38 byte wide strings (default: off - up to 29 bytes) */
+#define CMPLOG_U256 1
+
 /* If a redqueen pass finds more than one solution, try to combine them? */
 #define CMPLOG_COMBINE
 
@@ -523,5 +526,12 @@
 
 #define AFL_TXT_STRING_MAX_MUTATIONS 6
 
+/* IGNORE */
+#ifdef CMPLOG_U256
+  #define _CMPLOG_EXTRA 8
+#else
+  #define _CMPLOG_EXTRA 0
+#endif
+
 #endif                                                  /* ! _HAVE_CONFIG_H */
 
diff --git a/include/types.h b/include/types.h
index d6476d82..fbd53826 100644
--- a/include/types.h
+++ b/include/types.h
@@ -48,6 +48,8 @@ typedef uint128_t         u128;
 #define FS_ERROR_MMAP 16
 #define FS_ERROR_OLD_CMPLOG 32
 #define FS_ERROR_OLD_CMPLOG_QEMU 64
+#define FS_ERROR_U256CMPLOG1 128
+#define FS_ERROR_U256CMPLOG2 256
 
 /* Reporting options */
 #define FS_OPT_ENABLED 0x80000001
@@ -56,6 +58,7 @@ typedef uint128_t         u128;
 #define FS_OPT_AUTODICT 0x10000000
 #define FS_OPT_SHDMEM_FUZZ 0x01000000
 #define FS_OPT_NEWCMPLOG 0x02000000
+#define FS_OPT_U256CMPLOG 0x04000000
 #define FS_OPT_OLD_AFLPP_WORKAROUND 0x0f000000
 // FS_OPT_MAX_MAPSIZE is 8388608 = 0x800000 = 2^23 = 1 << 23
 #define FS_OPT_MAX_MAPSIZE ((0x00fffffeU >> 1) + 1)
diff --git a/instrumentation/afl-compiler-rt.o.c b/instrumentation/afl-compiler-rt.o.c
index 85ee9f71..ace1c9c8 100644
--- a/instrumentation/afl-compiler-rt.o.c
+++ b/instrumentation/afl-compiler-rt.o.c
@@ -856,6 +856,7 @@ static void __afl_start_snapshots(void) {
   if (__afl_map_size <= FS_OPT_MAX_MAPSIZE)
     status |= (FS_OPT_SET_MAPSIZE(__afl_map_size) | FS_OPT_MAPSIZE);
   if (__afl_dictionary_len && __afl_dictionary) { status |= FS_OPT_AUTODICT; }
+  if (1 == CMPLOG_U256 && __afl_cmp_map) { status |= FS_OPT_U256CMPLOG; }
   memcpy(tmp, &status, 4);
 
   if (write(FORKSRV_FD + 1, tmp, 4) != 4) { return; }
@@ -2290,11 +2291,11 @@ void __cmplog_rtn_hook_strn(u8 *ptr1, u8 *ptr2, u64 len) {
   // fprintf(stderr, "RTN1 %p %p %u\n", ptr1, ptr2, len);
   if (likely(!__afl_cmp_map)) return;
   if (unlikely(!len)) return;
-  int len0 = MIN(len, 31);
+  int len0 = MIN(len, 31 + _CMPLOG_EXTRA);
   int len1 = strnlen(ptr1, len0);
-  if (len1 < 31) len1 = area_is_valid(ptr1, len1 + 1);
+  if (len1 < 31 + _CMPLOG_EXTRA) len1 = area_is_valid(ptr1, len1 + 1);
   int len2 = strnlen(ptr2, len0);
-  if (len2 < 31) len2 = area_is_valid(ptr2, len2 + 1);
+  if (len2 < 31 + _CMPLOG_EXTRA) len2 = area_is_valid(ptr2, len2 + 1);
   int l = MAX(len1, len2);
   if (l < 2) return;
 
@@ -2384,7 +2385,7 @@ void __cmplog_rtn_hook(u8 *ptr1, u8 *ptr2) {
 
   /*
     u32 i;
-    if (area_is_valid(ptr1, 31) <= 0 || area_is_valid(ptr2, 31) <= 0) return;
+    if (area_is_valid(ptr1, 31 + _CMPLOG_EXTRA) <= 0 || area_is_valid(ptr2, 31 + _CMPLOG_EXTRA) <= 0) return;
     fprintf(stderr, "rtn arg0=");
     for (i = 0; i < 32; i++)
       fprintf(stderr, "%02x", ptr1[i]);
@@ -2397,10 +2398,10 @@ void __cmplog_rtn_hook(u8 *ptr1, u8 *ptr2) {
   // fprintf(stderr, "RTN1 %p %p\n", ptr1, ptr2);
   if (likely(!__afl_cmp_map)) return;
   int l1, l2;
-  if ((l1 = area_is_valid(ptr1, 31)) <= 0 ||
-      (l2 = area_is_valid(ptr2, 31)) <= 0)
+  if ((l1 = area_is_valid(ptr1, 31 + _CMPLOG_EXTRA)) <= 0 ||
+      (l2 = area_is_valid(ptr2, 31 + _CMPLOG_EXTRA)) <= 0)
     return;
-  int len = MIN(31, MIN(l1, l2));
+  int len = MIN(31 + _CMPLOG_EXTRA, MIN(l1, l2));
 
   // fprintf(stderr, "RTN2 %u\n", len);
   uintptr_t k = (uintptr_t)__builtin_return_address(0);
@@ -2449,7 +2450,7 @@ void __cmplog_rtn_hook_n(u8 *ptr1, u8 *ptr2, u64 len) {
 #if 0
   /*
     u32 i;
-    if (area_is_valid(ptr1, 31) <= 0 || area_is_valid(ptr2, 31) <= 0) return;
+    if (area_is_valid(ptr1, 31 + _CMPLOG_EXTRA) <= 0 || area_is_valid(ptr2, 31 + _CMPLOG_EXTRA) <= 0) return;
     fprintf(stderr, "rtn_n len=%u arg0=", len);
     for (i = 0; i < len; i++)
       fprintf(stderr, "%02x", ptr1[i]);
@@ -2462,7 +2463,7 @@ void __cmplog_rtn_hook_n(u8 *ptr1, u8 *ptr2, u64 len) {
   // fprintf(stderr, "RTN1 %p %p %u\n", ptr1, ptr2, len);
   if (likely(!__afl_cmp_map)) return;
   if (unlikely(!len)) return;
-  int l = MIN(31, len);
+  int l = MIN(31 + _CMPLOG_EXTRA, len);
 
   if ((l = area_is_valid(ptr1, l)) <= 0 || (l = area_is_valid(ptr2, l)) <= 0)
     return;
diff --git a/src/afl-forkserver.c b/src/afl-forkserver.c
index 07f5a1a9..94bca9d0 100644
--- a/src/afl-forkserver.c
+++ b/src/afl-forkserver.c
@@ -469,6 +469,12 @@ static void report_error_and_exit(int error) {
 
   switch (error) {
 
+    case FS_ERROR_U256CMPLOG1:
+      FATAL("afl-fuzz was compiled for CMPLOG_U256, but the target was not");
+      break;
+    case FS_ERROR_U256CMPLOG2:
+      FATAL("the target was compiled for CMPLOG_U256, but afl-fuzz was not");
+      break;
     case FS_ERROR_MAP_SIZE:
       FATAL(
           "AFL_MAP_SIZE is not set and fuzzing target reports that the "
@@ -1026,9 +1032,27 @@ void afl_fsrv_start(afl_forkserver_t *fsrv, char **argv,
     if ((status & FS_OPT_ENABLED) == FS_OPT_ENABLED) {
 
       // workaround for recent AFL++ versions
-      if ((status & FS_OPT_OLD_AFLPP_WORKAROUND) == FS_OPT_OLD_AFLPP_WORKAROUND)
+      if ((status & FS_OPT_OLD_AFLPP_WORKAROUND) ==
+          FS_OPT_OLD_AFLPP_WORKAROUND) {
+
         status = (status & 0xf0ffffff);
 
+      }
+
+      if (fsrv->cmplog_binary && CMPLOG_U256 == 1 &&
+          (status & FS_OPT_U256CMPLOG) == 0) {
+
+        report_error_and_exit(FS_ERROR_U256CMPLOG1);
+
+      }
+
+      if (fsrv->cmplog_binary && CMPLOG_U256 == 0 &&
+          (status & FS_OPT_U256CMPLOG)) {
+
+        report_error_and_exit(FS_ERROR_U256CMPLOG2);
+
+      }
+
       if ((status & FS_OPT_NEWCMPLOG) == 0 && fsrv->cmplog_binary) {
 
         if (fsrv->qemu_mode || fsrv->frida_mode) {
diff --git a/src/afl-fuzz-redqueen.c b/src/afl-fuzz-redqueen.c
index db4991db..8ea23daf 100644
--- a/src/afl-fuzz-redqueen.c
+++ b/src/afl-fuzz-redqueen.c
@@ -2010,8 +2010,9 @@ static u8 rtn_extend_encoding(afl_state_t *afl, u8 entry,
 
   }
 
-  if (l0 == 0 || l1 == 0 || ol0 == 0 || ol1 == 0 || l0 > 31 || l1 > 31 ||
-      ol0 > 31 || ol1 > 31) {
+  if (l0 == 0 || l1 == 0 || ol0 == 0 || ol1 == 0 || l0 > 31 + _CMPLOG_EXTRA ||
+      l1 > 31 + _CMPLOG_EXTRA || ol0 > 31 + _CMPLOG_EXTRA ||
+      ol1 > 31 + _CMPLOG_EXTRA) {
 
     l0 = ol0 = hshape;
 
@@ -2121,7 +2122,8 @@ static u8 rtn_extend_encoding(afl_state_t *afl, u8 entry,
     u32 tob64 = 0, fromb64 = 0;
     u32 from_0 = 0, from_x = 0, from_X = 0, from_slash = 0, from_up = 0;
     u32 to_0 = 0, to_x = 0, to_slash = 0, to_up = 0;
-    u8  xor_val[32], arith_val[32], tmp[48];
+    u8  xor_val[32 + _CMPLOG_EXTRA], arith_val[32 + _CMPLOG_EXTRA],
+        tmp[48 + (_CMPLOG_EXTRA << 1)];
 
     idx = saved_idx;
     its_len = saved_its_len;