# GF21: C preprocessor "/lib/cpp" fails sanity check

## Maedhros

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Q: Why am I getting the following error?

```
configure: error: C preprocessor "/lib/cpp" fails sanity check
```

A: This problem is very probably caused by the lack of kernel headers on your system. 

If you're doing a stage 1 install, this might mean you've missed out the bootstrap phase, which is described here: (Example from the x86 installation handbook).

If you've finished the installation and this error still occurs, then you should install the headers manually. 

```
emerge --ask --verbose --oneshot linux-headers
```

Edit: Removed reference to now-defunct linux26-headers.

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