diff --git a/bash_completion b/bash_completion
index bf42e00885b..8d2030250cd 100644
--- a/bash_completion
+++ b/bash_completion
@@ -2181,15 +2181,22 @@ _comp_compgen_fstypes()
 _comp_abspath()
 {
     REPLY=$1
-    case $REPLY in
-        /*) ;;
-        ../*) REPLY=$PWD/${REPLY:3} ;;
-        *) REPLY=$PWD/$REPLY ;;
-    esac
-    while [[ $REPLY == */./* ]]; do
-        REPLY=${REPLY//\/.\//\/}
-    done
+    [[ $REPLY == /* ]] || REPLY=$PWD/$REPLY
     REPLY=${REPLY//+(\/)/\/}
+    while true; do
+        # Process "." and "..".  To avoid reducing "/../../ => /", we convert
+        # "/*/../" one by one. "/.."  at the beginning is ignored. Then, /*/../
+        # in the middle is processed.  Finally, /*/.. at the end is removed.
+        case $REPLY in
+            */./*) REPLY=${REPLY//\/.\//\/} ;;
+            */.) REPLY=${REPLY%/.} ;;
+            /..?(/*)) REPLY=${REPLY#/..} ;;
+            */+([^/])/../*) REPLY=${REPLY/\/+([^\/])\/..\//\/} ;;
+            */+([^/])/..) REPLY=${REPLY%/+([^/])/..} ;;
+            *) break ;;
+        esac
+    done
+    [[ $REPLY ]] || REPLY=/
 }
 
 # Get real command.
@@ -3125,6 +3132,18 @@ _comp_complete_minimal()
 # https://lists.gnu.org/archive/html/bug-bash/2012-01/msg00045.html
 complete -F _comp_complete_minimal ''
 
+# Initialize the variable "_comp__base_directory"
+# @var[out] _comp__base_directory
+_comp__init_base_directory()
+{
+    local REPLY
+    _comp_abspath "${BASH_SOURCE[0]-./bash_completion}"
+    _comp__base_directory=${REPLY%/*}
+    [[ $_comp__base_directory ]] || _comp__base_directory=/
+    unset -f "$FUNCNAME"
+}
+_comp__init_base_directory
+
 # @since 2.12
 _comp_load()
 {
@@ -3177,11 +3196,7 @@ _comp_load()
     # we want to prefer in-tree completions over ones possibly coming with a
     # system installed bash-completion. (Due to usual install layouts, this
     # often hits the correct completions in system installations, too.)
-    if [[ $BASH_SOURCE == */* ]]; then
-        dirs+=("${BASH_SOURCE%/*}/completions")
-    else
-        dirs+=(./completions)
-    fi
+    dirs+=("$_comp__base_directory/completions")
 
     # 3) From bin directories extracted from the specified path to the command,
     # the real path to the command, and $PATH
@@ -3323,12 +3338,10 @@ _comp__init_collect_startup_configs()
         # run-in-place-from-git-clone setups.  Notably we do it after the
         # system location here, in order to prefer in-tree variables and
         # functions.
-        if [[ ${base_path%/*} == */share/bash-completion ]]; then
-            compat_dir=${base_path%/share/bash-completion/*}/etc/bash_completion.d
-        elif [[ $base_path == */* ]]; then
-            compat_dir="${base_path%/*}/bash_completion.d"
+        if [[ $_comp__base_directory == */share/bash-completion ]]; then
+            compat_dir=${_comp__base_directory%/share/bash-completion}/etc/bash_completion.d
         else
-            compat_dir=./bash_completion.d
+            compat_dir=$_comp__base_directory/bash_completion.d
         fi
         [[ ${compat_dirs[0]} == "$compat_dir" ]] ||
             compat_dirs+=("$compat_dir")
diff --git a/test/t/unit/test_unit_abspath.py b/test/t/unit/test_unit_abspath.py
index 97d506cce3a..88c9f6b5d32 100644
--- a/test/t/unit/test_unit_abspath.py
+++ b/test/t/unit/test_unit_abspath.py
@@ -46,7 +46,7 @@ def test_relative(self, bash, functions):
         )
         assert output.strip().endswith("/shared/foo/bar")
 
-    def test_cwd(self, bash, functions):
+    def test_cwd1(self, bash, functions):
         output = assert_bash_exec(
             bash,
             "__tester ./foo/./bar",
@@ -55,7 +55,34 @@ def test_cwd(self, bash, functions):
         )
         assert output.strip().endswith("/shared/foo/bar")
 
-    def test_parent(self, bash, functions):
+    def test_cwd2(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /.",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/"
+
+    def test_cwd3(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /foo/.",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/foo"
+
+    def test_cwd4(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /././.",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/"
+
+    def test_parent1(self, bash, functions):
         output = assert_bash_exec(
             bash,
             "__tester ../shared/foo/bar",
@@ -65,3 +92,102 @@ def test_parent(self, bash, functions):
         assert output.strip().endswith(
             "/shared/foo/bar"
         ) and not output.strip().endswith("../shared/foo/bar")
+
+    def test_parent2(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /foo/..",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/"
+
+    def test_parent3(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /..",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/"
+
+    def test_parent4(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /../foo/bar",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/foo/bar"
+
+    def test_parent5(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /../../foo/bar",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/foo/bar"
+
+    def test_parent6(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /foo/../bar",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/bar"
+
+    def test_parent7(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /foo/../../bar",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/bar"
+
+    def test_parent8(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /dir1/dir2/dir3/../dir4/../../foo",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/dir1/foo"
+
+    def test_parent9(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester //dir1/dir2///../foo",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/dir1/foo"
+
+    def test_parent10(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /dir1/dir2/dir3/..",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/dir1/dir2"
+
+    def test_parent11(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /dir1/dir2/dir3/../..",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/dir1"
+
+    def test_parent12(self, bash, functions):
+        output = assert_bash_exec(
+            bash,
+            "__tester /dir1/dir2/dir3/../../../..",
+            want_output=True,
+            want_newline=False,
+        )
+        assert output.strip() == "/"