diff --git a/mdbx.h b/mdbx.h
index ec38193c..8d5a6e2e 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -79,6 +79,7 @@ typedef DWORD mdbx_tid_t;
 #define MDBX_EROFS ERROR_FILE_READ_ONLY
 #define MDBX_ENOSYS ERROR_NOT_SUPPORTED
 #define MDBX_EIO ERROR_WRITE_FAULT
+#define MDBX_EPERM ERROR_INVALID_FUNCTION
 
 #else
 
@@ -97,6 +98,7 @@ typedef pthread_t mdbx_tid_t;
 #define MDBX_EROFS EROFS
 #define MDBX_ENOSYS ENOSYS
 #define MDBX_EIO EIO
+#define MDBX_EPERM EPERM
 #endif
 
 #ifdef _MSC_VER
diff --git a/src/mdbx.c b/src/mdbx.c
index 13768b29..417595ad 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -2434,6 +2434,9 @@ int mdbx_txn_begin(MDBX_env *env, MDBX_txn *parent, unsigned flags,
     return MDBX_PANIC;
   }
 
+  if (unlikely(!env->me_map))
+    return MDBX_EPERM;
+
   flags &= MDBX_TXN_BEGIN_FLAGS;
   flags |= env->me_flags & MDBX_WRITEMAP;