diff --git a/src/Psalm/Checker/Statements/Expression/Fetch/ArrayFetchChecker.php b/src/Psalm/Checker/Statements/Expression/Fetch/ArrayFetchChecker.php
index 19b01cc7b..38c324a6a 100644
--- a/src/Psalm/Checker/Statements/Expression/Fetch/ArrayFetchChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/Fetch/ArrayFetchChecker.php
@@ -158,7 +158,7 @@ class ArrayFetchChecker
                     $const_array_key_type = $array_type->getGenericKeyType();
                 }
 
-                if ($dim_var_id && !$const_array_key_type->isMixed()) {
+                if ($dim_var_id && !$const_array_key_type->isMixed() && !$stmt->dim->inferredType->isMixed()) {
                     $new_offset_type = clone $stmt->dim->inferredType;
                     $const_array_key_atomic_types = $const_array_key_type->getTypes();
                     $project_checker = $statements_checker->getFileChecker()->project_checker;
@@ -186,7 +186,11 @@ class ArrayFetchChecker
                             )) {
                                 $new_offset_type->removeType($offset_key);
                             }
-                        } else {
+                        } elseif (!TypeChecker::isContainedBy(
+                            $project_checker->codebase,
+                            $const_array_key_type,
+                            new Type\Union([$offset_atomic_type])
+                        )) {
                             $new_offset_type->removeType($offset_key);
                         }
                     }
diff --git a/tests/ConstantTest.php b/tests/ConstantTest.php
index 9f704aa5f..7fc5952bd 100644
--- a/tests/ConstantTest.php
+++ b/tests/ConstantTest.php
@@ -151,6 +151,46 @@ class ConstantTest extends TestCase
                         }
                     }',
             ],
+            'noExceptionsOnMixedArrayKey' => [
+                '<?php
+                    function finder(string $id) : ?object {
+                      if (rand(0, 1)) {
+                        return new A();
+                      }
+
+                      if (rand(0, 1)) {
+                        return new B();
+                      }
+
+                      return null;
+                    }
+                    class A {}
+                    class B {}
+                    class Foo
+                    {
+                        private const TYPES = [
+                            "type1" => A::class,
+                            "type2" => B::class,
+                        ];
+
+                        public function bar(array $data): void
+                        {
+                            if (!isset(self::TYPES[$data["type"]])) {
+                                throw new \InvalidArgumentException("Unknown type");
+                            }
+
+                            $class = self::TYPES[$data["type"]];
+
+                            $ret = finder($data["id"]);
+
+                            if (!$ret || !$ret instanceof $class) {
+                                throw new \InvalidArgumentException;
+                            }
+                        }
+                    }',
+                'assertions' => [],
+                'error_levels' => ['MixedArgument', 'MixedArrayOffset', 'MixedAssignment'],
+            ],
         ];
     }