diff --git a/src/Psalm/Internal/Type/TemplateStandinTypeReplacer.php b/src/Psalm/Internal/Type/TemplateStandinTypeReplacer.php
index 91a3e8acf..a01b5cf66 100644
--- a/src/Psalm/Internal/Type/TemplateStandinTypeReplacer.php
+++ b/src/Psalm/Internal/Type/TemplateStandinTypeReplacer.php
@@ -88,7 +88,7 @@ class TemplateStandinTypeReplacer
             }
 
             if (!$atomic_types) {
-                throw new \UnexpectedValueException('Cannot remove all keys');
+                return $union_type;
             }
 
             if (count($atomic_types) > 1) {
diff --git a/tests/Template/ClassTemplateTest.php b/tests/Template/ClassTemplateTest.php
index 2c1d1596a..2a04b8b49 100644
--- a/tests/Template/ClassTemplateTest.php
+++ b/tests/Template/ClassTemplateTest.php
@@ -3370,7 +3370,7 @@ class ClassTemplateTest extends TestCase
                         $wm[$ex] = 42;
                     }
                 ',
-            ]
+            ],
         ];
     }
 
@@ -4010,6 +4010,29 @@ class ClassTemplateTest extends TestCase
                     takesA($child);',
                 'error_message' => 'InvalidArgument',
             ],
+            'noCrashTemplatedClosure' => [
+                '<?php
+                    /**
+                     * @template TCallback as Closure():string
+                     */
+                    class A {
+                        /** @var TCallback */
+                        private $callback;
+
+                        /** @param TCallback $callback */
+                        public function __construct(Closure $callback) {
+                            $this->callback = $callback;
+                        }
+
+                        /** @param TCallback $callback */
+                        public function setCallback(Closure $callback): void {
+                            $this->callback = $callback;
+                        }
+                    }
+                    $a = new A(function() { return "a";});
+                    $a->setCallback(function() { return "b";});',
+                'error_message' => 'InvalidScalarArgument',
+            ],
         ];
     }
 }