diff --git a/tests/checks/git.fish b/tests/checks/git.fish
index 6cebc2c4f..5ffcc9bad 100644
--- a/tests/checks/git.fish
+++ b/tests/checks/git.fish
@@ -3,6 +3,15 @@
 # e.g. the fish_git_prompt variable handlers test `status is-interactive`.
 #REQUIRES: command -v git
 
+# Tests run from git (e.g. git rebase --exec 'ninja test'...) inherit a weird git environment.
+# Ensure that no git environment variables are inherited.
+for varname in (set -x | string match 'GIT_*' | string replace -r ' .*' '')
+   set -e $varname
+end
+
+# Also ensure that git-core is not in $PATH, as this adds weird git commands like `git-add--interactive`.
+set PATH (string match --invert '*git-core*' -- $PATH)
+
 # Do some tests with `git` - completions are interesting,
 # but prompts would also be possible.