diff --git a/Lib/compression/zstd/_zstdfile.py b/Lib/compression/zstd/_zstdfile.py
index 26d7c9006375fb..f504c92d1fa143 100644
--- a/Lib/compression/zstd/_zstdfile.py
+++ b/Lib/compression/zstd/_zstdfile.py
@@ -325,11 +325,11 @@ def open(file, /, mode='rb', *, level=None, options=None, zstd_dict=None,
     """
 
     text_mode = 't' in mode
-    mode = mode.replace('t', '')
 
     if text_mode:
         if 'b' in mode:
             raise ValueError(f'Invalid mode: {mode!r}')
+        mode = mode.replace('t', '')
     else:
         if encoding is not None:
             raise ValueError('Argument "encoding" not supported in binary mode')
diff --git a/Misc/NEWS.d/next/Library/2026-11-09-23-37-08.gh-issue-161730.hh7MVs.rst b/Misc/NEWS.d/next/Library/2026-11-09-23-37-08.gh-issue-161730.hh7MVs.rst
new file mode 100644
index 00000000000000..db673f4e95ea14
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-11-09-23-37-08.gh-issue-161730.hh7MVs.rst
@@ -0,0 +1,2 @@
+Fix :func:`compression.zstd.open` naming the wrong mode in the error message
+for an invalid mode that contains both ``'t'`` and ``'b'``.