diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index a61b6ed59a..76181e8714 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1981,6 +1981,10 @@ _git_diff ()
 		esac
 		__git_complete_revlist_file
 	fi
+
+	if [ ${#COMPREPLY[@]} -eq 0 ]; then
+		__git_complete_index_file ""
+	fi
 }
 
 __git_mergetools_common="diffuse diffmerge ecmerge emerge kdiff3 meld opendiff
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 55dc9eabfc..32e5d484c7 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -2663,6 +2663,7 @@ test_expect_success 'setup for integration tests' '
 	echo content >file1 &&
 	echo more >file2 &&
 	git add file1 file2 &&
+	echo untracked >file3 &&
 	git commit -m one &&
 	git branch mybranch &&
 	git tag mytag
@@ -2712,6 +2713,45 @@ test_expect_success 'git -C <path> checkout uses the right repo' '
 	EOF
 '
 
+test_expect_success 'git diff completes tracked paths when no refs match' '
+	# file1 and file2 are tracked but file3 is not
+	# there is no ref that begins with f
+	test_completion "git diff f" <<-\EOF &&
+	file1
+	file2
+	EOF
+	test_completion "git diff -- f" <<-\EOF
+	file1
+	file2
+	EOF
+'
+
+test_expect_success 'git -C <path> diff completes paths in specified repo' '
+	test_when_finished "rm -rf repo-for-diff" &&
+	git init repo-for-diff &&
+	echo content >repo-for-diff/otherfile &&
+	echo content >repo-for-diff/lostfile &&
+	git -C repo-for-diff add otherfile &&
+	git -C repo-for-diff add lostfile &&
+	git -C repo-for-diff commit -m otherfile &&
+	echo untracked >repo-for-diff/oops &&
+	rm -f repo-for-diff/lostfile &&
+
+	test_completion "git -C repo-for-diff diff o" <<-\EOF &&
+	otherfile
+	EOF
+	test_completion "git -C repo-for-diff diff l" <<-\EOF &&
+	lostfile
+	EOF
+
+	test_completion "git -C repo-for-diff diff -- o" <<-\EOF &&
+	otherfile
+	EOF
+	test_completion "git -C repo-for-diff diff -- l" <<-\EOF
+	lostfile
+	EOF
+'
+
 test_expect_success 'show completes all refs' '
 	test_completion "git show m" <<-\EOF
 	main Z