diff --git a/mypy/semanal.py b/mypy/semanal.py
index 024bb7960277..648207445f45 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -3327,7 +3327,10 @@ def name_not_defined(self, name: str, ctx: Context) -> None:
     def name_already_defined(self, name: str, ctx: Context,
                              original_ctx: Optional[SymbolTableNode] = None) -> None:
         if original_ctx:
-            extra_msg = ' on line {}'.format(original_ctx.node.get_line())
+            if original_ctx.node and original_ctx.node.get_line() != -1:
+                extra_msg = ' on line {}'.format(original_ctx.node.get_line())
+            else:
+                extra_msg = ' (line unavailable; possibly an import)'
         else:
             extra_msg = ''
         self.fail("Name '{}' already defined{}".format(name, extra_msg), ctx)