[WinError 1114] A dynamic link library (DLL) initialization routine failed

@seemethere

🐛 Describe the bug

PyTorch fails to import after PyQt on Windows

Description

Importing PyTorch after PyQt on Windows causes a DLL initialization error. The same code works if PyTorch is imported first.

This issue started occurring after upgrading from PyTorch 2.8.0 to 2.9.0.

Reproduction

This code fails:

from PyQt6.QtWidgets import QApplication
import torch

Result:

Traceback (most recent call last):
  File ""C:\...\abogen\abogen\test.py", line 3, in <module>
    import torch
  File ""C:\...\Lib\site-packages\torch\__init__.py", line 281, in <module>
    _load_dll_libraries()
  File ""C:\...\Lib\site-packages\torch\__init__.py", line 264, in _load_dll_libraries
    raise err
OSError: [WinError 1114] A dynamic link library (DLL) initialization routine failed. Error loading ""C:\...\Lib\site-packages\torch\lib\c10.dll" or one of its dependencies.

This code works:

import torch
from PyQt6.QtWidgets import QApplication

Result:

(imports successfully, no error)

Notes

Issue started after upgrading from PyTorch 2.8.0 to 2.9.0.
Affects Windows GUI applications using both PyTorch and PyQt

Note

Issue is still present in PyTorch 2.9.1

Versions

Collecting environment information...
PyTorch version: 2.9.0+cpu
Is debug build: False
CUDA used to build PyTorch: None
ROCM used to build PyTorch: N/A

OS: Microsoft Windows 11 Home (10.0.26200 64-bit)
GCC version: Could not collect
Clang version: Could not collect
CMake version: Could not collect
Libc version: N/A

Python version: 3.12.12 [MSC v.1944 64 bit (AMD64)] (64-bit runtime)
Python platform: Windows-11-10.0.26200-SP0
Is CUDA available: False
CUDA runtime version: No CUDA
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: No CUDA
Nvidia driver version: No CUDA
cuDNN version: No CUDA
Is XPU available: False
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: True

Versions of relevant libraries:
[pip3] intel-openmp==2021.4.0
[pip3] mkl==2021.4.0
[pip3] numpy==2.3.4
[pip3] tbb==2021.13.1
[pip3] torch==2.9.0
[pip3] torchaudio==2.9.0
[pip3] torchvision==0.24.0
[conda] Could not collect

cc @seemethere @malfet @atalman @peterjc123 @mszhanyi @skyline75489 @nbcsm @iremyux @Blackhex

Hello, I confirm this bug on my side too.

same error here, windows 10 without PyQt, dependency walker shows nothing except api-ms-win missing

somehow it happens today on my site as well, even thought I solely install pandas and torch using uv add, and then import torch in main.py only.

OS: Windows 11
Python Version: 3.12.9

...\.venv\Lib\site-packages\torch\__init__.py", line 264, in _load_dll_libraries
    raise err
OSError: [WinError 1114] A dynamic link library (DLL) initialization routine failed. Error loading "...\.venv\Lib\site
-packages\torch\lib\c10.dll" or one of its dependencies.

Note: I tried on my Mac, it's totally fine.

@RueiHuanRao

@RueiHuanRao @Manoa1911 @fteicht

There are 4 solutions so far:

Solution 1: Downgrade PyTorch to `2.8.0`

pip install torch==2.8.0 torchvision==0.23.0 torchaudio==2.8.0

Solution 2: Pre-load `c10.dll`

# Fix PyTorch DLL loading issue on Windows
# You need to add this at the beginning, before importing torch and other conflicting modules

import os
import platform
if platform.system() == "Windows":
    import ctypes
    from importlib.util import find_spec
    try:
        if (spec := find_spec("torch")) and spec.origin and os.path.exists(
            dll_path := os.path.join(os.path.dirname(spec.origin), "lib", "c10.dll")
        ):
            ctypes.CDLL(os.path.normpath(dll_path))
    except Exception:
        pass

# Testing
from PyQt6.QtWidgets import QApplication
import torch

# Imports successfully

Solution 3: Import torch before PyQt

import torch # imported before PyQt
from PyQt6.QtWidgets import QApplication

Solution 4: Install latest Microsoft Visual C++

https://learn.microsoft.com/en-us/cpp/windows/latest-supported-vc-redist

This also happens with PyQt5.

Issue persists with PyQt5 + torch 2.9.0. Uninstalling torch and downgrading to 2.8.0 fixed it for me.

@denizsafak

@denizsafak Thank you! I'll have a try!

@denizsafak

Same issue here.
This works:

import torch
from PyQt6.QtWidgets import QApplication

Even I don't need to import torch in this specific file, pre-importing it before PyQt will make the app run. @denizsafak How did you find out this? Such a weird solution.

@OnCodeDeny

@OnCodeDeny after updating PyTorch, my app started throwing this error. A simple test script that just imported torch worked fine, so I dug deeper and found out the issue was caused by this conflict with PyQt.

Same issues with me OSError: [WinError 1114] A dynamic link library (DLL) initialization routine failed. Error loading "C:\Users\Asif Ali\Desktop\Email-Warmup-Tool\app\venv\lib\site-packages\torch\lib\c10.dll" or one of its dependencies

fix: centralize Windows PyTorch DLL pre-loading via advanced library

(I think)
I am using PyQt5, and some langchain modules for an AI Agent. Actually, when some packages want the .dll files to execute properly, windows load them in the process's address space. When another package wants the same .dll file, it is not loaded again, and the same pre-loaded file is used for that particular package as well. Torch packages uses newer version of the dll library c10.dll (and probably numerous others as well). But PyQt5 uses the same older vresions. Now, the issue arises when the PyQt5 is placed above the langchain modules, loading the older versions of this .dll in the process's address space. When the control imports the torch module, and tries to use the same older version of that .dll file, it fails to accept that version, and triggers that error.
Placing the PyQt5 module below langchain modules solves the error in the way, that the newer module of the .dll is loaded in the memory, and both the packages agree to use this newer version, solving the issue.

Fix torch dep

Fix torch dep (#576)

Solution 3: Import torch before PyQt - it works!

Python 3.13.15
torch==2.14.0+cu132
torchvision==0.29.0+cu132

fix(thelip-server): torch first and pinned to 2.8.0; explain a DLL fa…

Note: For those of us who don't use PyQt but have this error: running from terminal - instead of from the IDE (PyCharm) - works for me, and debugging works if I set the "debugpy" debugger mode instead of "pydevd" (the default) in Settings > Python > Debugger. Execution with Run from PyCharm still doesn't work in this way though.

Same here with PyTorch 2.14.1 + torchvision 0.29.1 (cu126). Importing PyQt5 before YOLO didn’t help. The script runs fine, but the PyInstaller EXE fails with the c10.dll error. Downgrading to torch 2.8.0 + torchvision 0.23.0 (cu126) fixed it (y)

@DToxeV

@DToxeV, have you tried PyTorch 2.15?

Fixed by #196987

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[WinError 1114] A dynamic link library (DLL) initialization routine failed #166628

🐛 Describe the bug

PyTorch fails to import after PyQt on Windows

Description

Reproduction

This code fails:

This code works:

Notes

Versions

Solution 1: Downgrade PyTorch to `2.8.0`

Solution 2: Pre-load `c10.dll`

Solution 3: Import torch before PyQt

Solution 4: Install latest Microsoft Visual C++

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[WinError 1114] A dynamic link library (DLL) initialization routine failed #166628

Description

🐛 Describe the bug

PyTorch fails to import after PyQt on Windows

Description

Reproduction

This code fails:

This code works:

Notes

Versions

Activity

fteicht commented on Oct 31, 2025

Manoa1911 commented on Nov 1, 2025

RueiHuanRao commented on Nov 3, 2025

denizsafak commented on Nov 3, 2025

Solution 1: Downgrade PyTorch to 2.8.0

Solution 2: Pre-load c10.dll

Solution 3: Import torch before PyQt

Solution 4: Install latest Microsoft Visual C++

isaac-bender commented on Nov 3, 2025

NelsonGoosman commented on Nov 4, 2025

RueiHuanRao commented on Nov 4, 2025

OnCodeDeny commented on Nov 5, 2025

denizsafak commented on Nov 5, 2025

aasifdemand commented on Nov 8, 2025

AmmarMujtaba commented on Nov 12, 2025

45 remaining items

infnetdanpro commented on Sep 9, 2026

tomeeeS commented on Sep 29, 2026

DToxeV commented on Oct 14, 2026

taras-janea commented on Oct 14, 2026

taras-janea commented on Oct 16, 2026

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Issue actions

Solution 1: Downgrade PyTorch to `2.8.0`

Solution 2: Pre-load `c10.dll`