How to avoid being (falsely) accused of plagiarism when reusing notations and definitions I'm currently writing a paper of my results in a field of pure mathematics.

My work is a generalization of an already existing result, which is not mine. My adviser and I think that there is a substantial differences between my result and the already existing result, and so it's worth a publication.

Since I'm generalizing an already existing paper it will be very convenient both for me and the readers that I will use the same notations and definitions as in the other paper. So I wrote those down and cited the other authors. 

The part of definitions and notations is roughly 10%-15% of the whole paper, and even though I properly cited the other authors, I'm worried to be accused of plagiarism by the "automatic plagiarism detector", which I heard most journals use.

How can I avoid being falsely accused for plagiarism?
It is generally known that definitions and restated theorems can cause significant textual overlap between papers to an extent that could be considered problematic. There is no point in worrying about automatic plagiarism checks for journal submissions: If a journal is relying on that alone without an editor checking, it is not a reasonable journal to submit to anyway.