diff --git a/src/mdbx.c b/src/mdbx.c
index 1ff535b7..c5148a80 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -5024,7 +5024,7 @@ fail:
 
 int __cold mdbx_env_get_maxkeysize(MDBX_env *env) {
   if (!env || env->me_signature != MDBX_ME_SIGNATURE || !env->me_maxkey_limit)
-    return -MDBX_EINVAL;
+    return (MDBX_EINVAL > 0) ? -MDBX_EINVAL : MDBX_EINVAL;
   return env->me_maxkey_limit;
 }
 
@@ -11538,7 +11538,7 @@ int __cold mdbx_reader_list(MDBX_env *env, MDBX_msg_func *func, void *ctx) {
   int rc = 0, first = 1;
 
   if (unlikely(!env || !func))
-    return -MDBX_EINVAL;
+    return (MDBX_EINVAL > 0) ? -MDBX_EINVAL : MDBX_EINVAL;
 
   if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
     return MDBX_EBADSIGN;
@@ -11848,7 +11848,7 @@ __attribute__((no_sanitize_thread, noinline))
 int mdbx_txn_straggler(MDBX_txn *txn, int *percent)
 {
   if (unlikely(!txn))
-    return -MDBX_EINVAL;
+    return (MDBX_EINVAL > 0) ? -MDBX_EINVAL : MDBX_EINVAL;
 
   if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
     return MDBX_EBADSIGN;
@@ -12501,6 +12501,17 @@ int mdbx_dbi_sequence(MDBX_txn *txn, MDBX_dbi dbi, uint64_t *result,
 
 /*----------------------------------------------------------------------------*/
 
+__cold intptr_t mdbx_limits_keysize_max(intptr_t pagesize) {
+  if (pagesize < 1)
+    pagesize = (intptr_t)mdbx_syspagesize();
+  else if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
+                    pagesize > (intptr_t)MAX_PAGESIZE ||
+                    !mdbx_is_power2((size_t)pagesize)))
+    return (MDBX_EINVAL > 0) ? -MDBX_EINVAL : MDBX_EINVAL;
+
+  return mdbx_maxkey(mdbx_nodemax(pagesize));
+}
+
 __cold int mdbx_limits_pgsize_min(void) { return MIN_PAGESIZE; }
 
 __cold int mdbx_limits_pgsize_max(void) { return MAX_PAGESIZE; }
@@ -12511,7 +12522,7 @@ __cold intptr_t mdbx_limits_dbsize_min(intptr_t pagesize) {
   else if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                     pagesize > (intptr_t)MAX_PAGESIZE ||
                     !mdbx_is_power2((size_t)pagesize)))
-    return -MDBX_EINVAL;
+    return (MDBX_EINVAL > 0) ? -MDBX_EINVAL : MDBX_EINVAL;
 
   return MIN_PAGENO * pagesize;
 }
@@ -12522,7 +12533,7 @@ __cold intptr_t mdbx_limits_dbsize_max(intptr_t pagesize) {
   else if (unlikely(pagesize < (intptr_t)MIN_PAGESIZE ||
                     pagesize > (intptr_t)MAX_PAGESIZE ||
                     !mdbx_is_power2((size_t)pagesize)))
-    return -MDBX_EINVAL;
+    return (MDBX_EINVAL > 0) ? -MDBX_EINVAL : MDBX_EINVAL;
 
   const uint64_t limit = MAX_PAGENO * (uint64_t)pagesize;
   return (limit < (intptr_t)MAX_MAPSIZE) ? (intptr_t)limit