diff --git a/flit_core/flit_core/common.py b/flit_core/flit_core/common.py
index 828b26b8..32c2a0da 100644
--- a/flit_core/flit_core/common.py
+++ b/flit_core/flit_core/common.py
@@ -128,10 +128,13 @@ def get_docstring_and_version_via_ast(target):
     for child in node.body:
         # Only use the version from the given module if it's a simple
         # string assignment to __version__
-        is_version_str = (isinstance(child, ast.Assign) and
-                          len(child.targets) == 1 and
-                          child.targets[0].id == "__version__" and
-                          isinstance(child.value, ast.Str))
+        is_version_str = (
+                isinstance(child, ast.Assign)
+                and len(child.targets) == 1
+                and isinstance(child.targets[0], ast.Name)
+                and child.targets[0].id == "__version__"
+                and isinstance(child.value, ast.Str)
+        )
         if is_version_str:
             version = child.value.s
             break
diff --git a/flit_core/flit_core/tests/samples/module2.py b/flit_core/flit_core/tests/samples/module2.py
index cc83e39f..70c868b3 100644
--- a/flit_core/flit_core/tests/samples/module2.py
+++ b/flit_core/flit_core/tests/samples/module2.py
@@ -2,4 +2,9 @@
 Docstring formatted like this.
 """
 
+a = {}
+# An assignment to a subscript (a['test']) broke introspection
+# https://github.com/takluyver/flit/issues/343
+a['test'] = 6
+
 __version__ = '7.0'