diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index e19d48f4f5e7..35371de155d7 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -895,7 +895,8 @@ def try_infer_partial_type(self, e: CallExpr) -> None:
                 return
             var, partial_types = ret
             typ = self.try_infer_partial_value_type_from_call(e, callee.name, var)
-            if typ is not None:
+            # Var may be deleted from partial_types in try_infer_partial_value_type_from_call
+            if typ is not None and var in partial_types:
                 var.type = typ
                 del partial_types[var]
         elif isinstance(callee.expr, IndexExpr) and isinstance(callee.expr.base, RefExpr):
diff --git a/test-data/unit/check-inference.test b/test-data/unit/check-inference.test
index 331b110fded6..fc8113766f1a 100644
--- a/test-data/unit/check-inference.test
+++ b/test-data/unit/check-inference.test
@@ -1951,6 +1951,13 @@ class A:
 [out]
 main:4: error: "None" has no attribute "__iter__" (not iterable)
 
+[case testPartialTypeErrorSpecialCase4]
+# This used to crash.
+arr = []
+arr.append(arr.append(1))
+[builtins fixtures/list.pyi]
+[out]
+main:3: error: "append" of "list" does not return a value
 
 -- Multipass
 -- ---------