diff --git a/mdbx.h b/mdbx.h
index 1e9094fe..cdf15c23 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -1949,8 +1949,8 @@ LIBMDBX_API int mdbx_env_get_fd(MDBX_env *env, mdbx_filehandle_t *fd);
  * option.
  *
  * Legacy mdbx_env_set_mapsize() correspond to calling mdbx_env_set_geometry()
- * with the argument size_now=size and -1 (i.e. default) for all other
- * parameters.
+ * with the arguments size_lower, size_now, size_upper equal to the size
+ * and -1 (i.e. default) for all other parameters.
  *
  * [in] env               An environment handle returned by mdbx_env_create()
  *
diff --git a/src/elements/core.c b/src/elements/core.c
index d6a81a00..2a07bf12 100644
--- a/src/elements/core.c
+++ b/src/elements/core.c
@@ -6923,7 +6923,7 @@ bailout:
 }
 
 int __cold mdbx_env_set_mapsize(MDBX_env *env, size_t size) {
-  return mdbx_env_set_geometry(env, -1, size, -1, -1, -1, -1);
+  return mdbx_env_set_geometry(env, size, size, size, -1, -1, -1);
 }
 
 int __cold mdbx_env_set_maxdbs(MDBX_env *env, MDBX_dbi dbs) {