python
diff --git a/‎mypy/checker.py
Lines changed: 1 addition & 0 deletions b/‎mypy/checker.py
Lines changed: 1 addition & 0 deletions
diff --git a/‎mypy/semanal.py
Lines changed: 18 additions & 2 deletions b/‎mypy/semanal.py
Lines changed: 18 additions & 2 deletions
diff --git a/‎mypy/test/data/check-modules.test
Lines changed: 29 additions & 1 deletion b/‎mypy/test/data/check-modules.test
Lines changed: 29 additions & 1 deletion
@@ -1240,6 +1240,7 @@ def check_lvalue(self, lvalue: Node) -> Tuple[Type, IndexExpr, Var]:
         if self.is_definition(lvalue):
             if isinstance(lvalue, NameExpr):
                 inferred = cast(Var, lvalue.node)
+                assert isinstance(inferred, Var)
             else:
                 m = cast(MemberExpr, lvalue)
                 self.accept(m.expr)
 
@@ -2055,8 +2055,11 @@ def add_symbol(self, name: str, node: SymbolTableNode,
                              existing.node != node.node) and existing.kind != UNBOUND_IMPORTED:
                 # Modules can be imported multiple times to support import
                 # of multiple submodules of a package (e.g. a.x and a.y).
-                if not (existing.type and node.type and is_same_type(existing.type, node.type)):
-                    # Only report an error if the symbol collision provides a different type.
+                ok = False
+                # Only report an error if the symbol collision provides a different type.
+                if existing.type and node.type and is_same_type(existing.type, node.type):
+                    ok = True
+                if not ok:
                     self.name_already_defined(name, context)
             self.globals[name] = node
 
@@ -2222,11 +2225,24 @@ def process_nested_classes(self, outer_def: ClassDef) -> None:
                 self.process_nested_classes(node)
 
     def visit_import_from(self, node: ImportFrom) -> None:
+        # We can't bind module names during the first pass, as the target module might be
+        # unprocessed. However, we add dummy unbound imported names to the symbol table so
+        # that we at least know that the name refers to a module.
         for name, as_name in node.names:
             imported_name = as_name or name
             if imported_name not in self.sem.globals:
                 self.sem.add_symbol(imported_name, SymbolTableNode(UNBOUND_IMPORTED, None), node)
 
+    def visit_import(self, node: Import) -> None:
+        # This is similar to visit_import_from -- see the comment there.
+        for id, as_id in node.ids:
+            imported_id = as_id or id
+            if imported_id not in self.sem.globals:
+                self.sem.add_symbol(imported_id, SymbolTableNode(UNBOUND_IMPORTED, None), node)
+            else:
+                # If the previous symbol is a variable, this should take precedence.
+                self.sem.globals[imported_id] = SymbolTableNode(UNBOUND_IMPORTED, None)
+
     def visit_for_stmt(self, s: ForStmt) -> None:
         self.analyze_lvalue(s.index)
 
 
@@ -322,7 +322,6 @@ def xab(): pass
 [out]
 main:1: error: Cannot find module named 'xab'
 main:1: note: (Perhaps setting MYPYPATH would help)
-main:1: error: Name 'xab' already defined
 
 [case testAccessingUnknownModuleFromOtherModule]
 import x
@@ -605,6 +604,35 @@ m.f = 1 # E: Incompatible types in assignment (expression has type "int", variab
 def f(): pass
 [out]
 
+[case testConditionalImportAndAssignNoneToModule]
+if object():
+    import m
+else:
+    m = None
+m.f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "str"
+[file m.py]
+def f(x: str) -> None: pass
+[builtins fixtures/module.py]
+[out]
+
+[case testConditionalImportAndAssignInvalidToModule]
+if object():
+    import m
+else:
+    m = 1 # E: Incompatible types in assignment (expression has type "int", variable has type "module")
+[file m.py]
+[builtins fixtures/module.py]
+[out]
+
+[case testImportAndAssignToModule]
+import m
+m = None
+m.f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "str"
+[file m.py]
+def f(x: str) -> None: pass
+[builtins fixtures/module.py]
+[out]
+
 
 -- Test cases that simulate 'mypy -m modname'
 --