diff --git a/mdbx.h b/mdbx.h
index 8d5265d4..9285b236 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -1683,6 +1683,8 @@ LIBMDBX_API int mdbx_limits_pgsize_min(void);
 LIBMDBX_API int mdbx_limits_pgsize_max(void);
 LIBMDBX_API intptr_t mdbx_limits_dbsize_min(intptr_t pagesize);
 LIBMDBX_API intptr_t mdbx_limits_dbsize_max(intptr_t pagesize);
+LIBMDBX_API intptr_t mdbx_limits_keysize_max(intptr_t pagesize);
+LIBMDBX_API intptr_t mdbx_limits_txnsize_max(intptr_t pagesize);
 
 /*----------------------------------------------------------------------------*/
 /* attribute support functions for Nexenta */
diff --git a/src/mdbx.c b/src/mdbx.c
index c5148a80..80e6435e 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -5037,14 +5037,7 @@ int __cold mdbx_env_get_maxkeysize(MDBX_env *env) {
   (((pagesize)-PAGEHDRSZ) / sizeof(pgno_t) - 1)
 
 int mdbx_get_maxkeysize(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;
-
-  return mdbx_maxkey(mdbx_nodemax(pagesize));
+  return (int)mdbx_limits_keysize_max(pagesize);
 }
 
 static void __cold mdbx_setup_pagesize(MDBX_env *env, const size_t pagesize) {
@@ -12540,6 +12533,17 @@ __cold intptr_t mdbx_limits_dbsize_max(intptr_t pagesize) {
                                          : (intptr_t)MAX_MAPSIZE;
 }
 
+__cold intptr_t mdbx_limits_txnsize_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 pagesize * (MDBX_PNL_UM_SIZE - 1);
+}
+
 /*----------------------------------------------------------------------------*/
 /* attribute support functions for Nexenta */