diff --git a/packaging/tags.py b/packaging/tags.py
index 6b404b43..034c16bb 100644
--- a/packaging/tags.py
+++ b/packaging/tags.py
@@ -233,12 +233,13 @@ def _generic_abi() -> List[str]:
     # - linux:   '.cpython-310-x86_64-linux-gnu.so' => cp310
     # - mac:     '.cpython-310-darwin.so'           => cp310
     # - win:     '.cp310-win_amd64.pyd'             => cp310
-    # - pypy:    '.pypy38-pp73-x86_64-linux-gnu.so' => pypy38-pp73
+    # - pypy:    '.pypy38-pp73-x86_64-linux-gnu.so' => pypy38_pp73
     # - graalpy: '.graalpy-38-native-x86_64-darwin.dylib'
-    #                                               => graalpy-38-native
+    #                                               => graalpy_38_native
 
     ext_suffix = _get_config_var("EXT_SUFFIX", warn=True)
-    assert ext_suffix[0] == "."
+    if not isinstance(ext_suffix, str) or ext_suffix[0] != ".":
+        raise SystemError("invalid sysconfig.get_config_var('EXT_SUFFIX')")
     _, soabi, ext = ext_suffix.split(".")
     if soabi.startswith("cpython"):
         abi = "cp" + soabi.split("-")[1]
diff --git a/tests/test_tags.py b/tests/test_tags.py
index 873cf9be..c135da2e 100644
--- a/tests/test_tags.py
+++ b/tests/test_tags.py
@@ -845,9 +845,25 @@ def test__generic_abi_linux_cpython(self, monkeypatch):
     def test__generic_abi_jp(self, monkeypatch):
         config = {"EXT_SUFFIX": ".return exactly this.so"}
         monkeypatch.setattr(sysconfig, "get_config_var", config.__getitem__)
-        monkeypatch.setattr(tags, "interpreter_name", lambda: "other")
         assert tags._generic_abi() == ["return exactly this"]
 
+    def test__generic_abi_graal(self, monkeypatch):
+        config = {"EXT_SUFFIX": ".graalpy-38-native-x86_64-darwin.so"}
+        monkeypatch.setattr(sysconfig, "get_config_var", config.__getitem__)
+        assert tags._generic_abi() == ["graalpy_38_native"]
+
+    def test__generic_abi_none(self, monkeypatch):
+        config = {"EXT_SUFFIX": "..so"}
+        monkeypatch.setattr(sysconfig, "get_config_var", config.__getitem__)
+        assert tags._generic_abi() == []
+
+    def test__generic_abi_none(self, monkeypatch):
+        config = {"EXT_SUFFIX": "invalid"}
+        monkeypatch.setattr(sysconfig, "get_config_var", config.__getitem__)
+        with pytest.raises(SystemError) as e:
+            tags._generic_abi()
+        assert "EXT_SUFFIX" in str(e.value)
+
     def test__generic_abi_linux_pypy(self, monkeypatch):
         # issue gh-606
         config = {