diff --git a/pyupgrade/_plugins/shlex_join.py b/pyupgrade/_plugins/shlex_join.py
index 14067560..1718ff9a 100644
--- a/pyupgrade/_plugins/shlex_join.py
+++ b/pyupgrade/_plugins/shlex_join.py
@@ -39,7 +39,7 @@ def visit_Call(
     if (
             isinstance(node.func, ast.Attribute) and
             isinstance(node.func.value, ast.Constant) and
-            isinstance(node.func.value.value, str) and
+            node.func.value.value == ' ' and
             node.func.attr == 'join' and
             not node.keywords and
             len(node.args) == 1 and
diff --git a/tests/features/shlex_join_test.py b/tests/features/shlex_join_test.py
index fc6abe59..e3835f65 100644
--- a/tests/features/shlex_join_test.py
+++ b/tests/features/shlex_join_test.py
@@ -15,6 +15,12 @@
             (3, 8),
             id='quote from-imported',
         ),
+        pytest.param(
+            'import shlex\n'
+            '"wat".join(shlex.quote(arg) for arg in cmd)\n',
+            (3, 8),
+            id='not joined with space',
+        ),
         pytest.param(
             'import shlex\n'
             '" ".join(shlex.quote(arg) for arg in cmd)\n',