diff --git a/news/12401.bugfix.rst b/news/12401.bugfix.rst
new file mode 100644
index 00000000000..371f80011b3
--- /dev/null
+++ b/news/12401.bugfix.rst
@@ -0,0 +1 @@
+Fix exception with completions when COMP_CWORD is not set
diff --git a/src/pip/_internal/cli/autocompletion.py b/src/pip/_internal/cli/autocompletion.py
index e5950b90696..f3f70ac8553 100644
--- a/src/pip/_internal/cli/autocompletion.py
+++ b/src/pip/_internal/cli/autocompletion.py
@@ -17,6 +17,10 @@ def autocomplete() -> None:
     # Don't complete if user hasn't sourced bash_completion file.
     if "PIP_AUTO_COMPLETE" not in os.environ:
         return
+    # Don't complete if autocompletion environment variables
+    # are not present
+    if not os.environ.get("COMP_WORDS") or not os.environ.get("COMP_CWORD"):
+        return
     cwords = os.environ["COMP_WORDS"].split()[1:]
     cword = int(os.environ["COMP_CWORD"])
     try:
diff --git a/tests/functional/test_completion.py b/tests/functional/test_completion.py
index cc8583b1a38..94a25eea219 100644
--- a/tests/functional/test_completion.py
+++ b/tests/functional/test_completion.py
@@ -120,7 +120,12 @@ def autocomplete_script(
 
 class DoAutocomplete(Protocol):
     def __call__(
-        self, words: str, cword: str, cwd: Union[Path, str, None] = None
+        self,
+        words: str,
+        cword: str,
+        cwd: Union[Path, str, None] = None,
+        include_env: bool = True,
+        expect_error: bool = True,
     ) -> Tuple[TestPipResult, PipTestEnvironment]:
         ...
 
@@ -133,16 +138,21 @@ def autocomplete(
     autocomplete_script.environ["PIP_AUTO_COMPLETE"] = "1"
 
     def do_autocomplete(
-        words: str, cword: str, cwd: Union[Path, str, None] = None
+        words: str,
+        cword: str,
+        cwd: Union[Path, str, None] = None,
+        include_env: bool = True,
+        expect_error: bool = True,
     ) -> Tuple[TestPipResult, PipTestEnvironment]:
-        autocomplete_script.environ["COMP_WORDS"] = words
-        autocomplete_script.environ["COMP_CWORD"] = cword
+        if include_env:
+            autocomplete_script.environ["COMP_WORDS"] = words
+            autocomplete_script.environ["COMP_CWORD"] = cword
         result = autocomplete_script.run(
             "python",
             "-c",
             "from pip._internal.cli.autocompletion import autocomplete;"
             "autocomplete()",
-            expect_error=True,
+            expect_error=expect_error,
             cwd=cwd,
         )
 
@@ -160,6 +170,17 @@ def test_completion_for_unknown_shell(autocomplete_script: PipTestEnvironment) -
     assert error_msg in result.stderr, "tests for an unknown shell failed"
 
 
+def test_completion_without_env_vars(autocomplete: DoAutocomplete) -> None:
+    """
+    Test getting completion <path> after options in command
+    given absolute path
+    """
+    res, env = autocomplete(
+        words="pip install ", cword="", include_env=False, expect_error=False
+    )
+    assert res.stdout == "", "autocomplete function did not complete"
+
+
 def test_completion_alone(autocomplete_script: PipTestEnvironment) -> None:
     """
     Test getting completion for none shell, just pip completion