diff --git a/src/Psalm/Internal/Type/Comparator/UnionTypeComparator.php b/src/Psalm/Internal/Type/Comparator/UnionTypeComparator.php
index c997199d650..52ad18757f4 100644
--- a/src/Psalm/Internal/Type/Comparator/UnionTypeComparator.php
+++ b/src/Psalm/Internal/Type/Comparator/UnionTypeComparator.php
@@ -6,6 +6,7 @@
 use Psalm\Internal\Type\TypeExpander;
 use Psalm\Type\Atomic;
 use Psalm\Type\Atomic\TArrayKey;
+use Psalm\Type\Atomic\TCallable;
 use Psalm\Type\Atomic\TClassConstant;
 use Psalm\Type\Atomic\TFalse;
 use Psalm\Type\Atomic\TIntRange;
@@ -21,6 +22,10 @@
 use function array_pop;
 use function array_push;
 use function array_reverse;
+use function count;
+use function is_array;
+
+use const PHP_INT_MAX;
 
 /**
  * @internal
@@ -134,6 +139,48 @@ public static function isContainedBy(
                     continue;
                 }
 
+                // if params are specified
+                if ($container_type_part instanceof TCallable
+                    && is_array($container_type_part->params)
+                    && $input_type_part instanceof TCallable
+                ) {
+                    $container_all_param_count = count($container_type_part->params);
+                    $container_required_param_count = 0;
+                    foreach ($container_type_part->params as $index => $container_param) {
+                        if ($container_param->is_optional === false) {
+                            $container_required_param_count = $index + 1;
+                        }
+
+                        if ($container_param->is_variadic === true) {
+                            $container_all_param_count = PHP_INT_MAX;
+                        }
+                    }
+
+                    $input_required_param_count = 0;
+                    if (!is_array($input_type_part->params)) {
+                        // it's not declared, there can be an arbitrary number of params
+                        $input_all_param_count = PHP_INT_MAX;
+                    } else {
+                        $input_all_param_count = count($input_type_part->params);
+                        foreach ($input_type_part->params as $index => $input_param) {
+                            if ($input_param->is_optional === false) {
+                                $input_required_param_count = $index + 1;
+                            }
+
+                            if ($input_param->is_variadic === true) {
+                                $input_all_param_count = PHP_INT_MAX;
+                            }
+                        }
+                    }
+
+                    // too few or too many non-optional params provided in callback
+                    if ($container_required_param_count > $input_all_param_count
+                        || $container_all_param_count < $input_required_param_count
+                    ) {
+                        return false;
+                    }
+                }
+
                 if ($union_comparison_result) {
                     $atomic_comparison_result = new TypeComparisonResult();
                 } else {
diff --git a/tests/ArgTest.php b/tests/ArgTest.php
index de57435f0e9..2d16c1934dd 100644
--- a/tests/ArgTest.php
+++ b/tests/ArgTest.php
@@ -312,6 +312,40 @@ public function foo(int ...$values): array
                     }
                 ',
             ],
+            'variadicCallbackArgsCountMatch' => [
+                '<?php
+                /**
+                 * @param callable(string, string):void $callback
+                 * @return void
+                 */
+                function caller($callback) {}
+
+                /**
+                 * @param string ...$bar
+                 * @return void
+                 */
+                function foo(...$bar) {}
+
+                caller("foo");',
+            ],
+            'variadicCallableArgsCountMatch' => [
+                '<?php
+                    /**
+                     * @param callable(string, ...int):void $callback
+                     * @return void
+                     */
+                    function var_caller($callback) {}
+
+                    /**
+                     * @param string $a
+                     * @param int $b
+                     * @param int $c
+                     * @return void
+                     */
+                    function foo($a, $b, $c) {}
+
+                    var_caller("foo");',
+            ],
         ];
     }
 
@@ -733,6 +767,41 @@ public function __construct(
                 ',
                 'error_message' => 'TooFewArguments',
             ],
+            'callbackArgsCountMismatch' => [
+                '<?php
+                    /**
+                     * @param callable(string, string):void $callback
+                     * @return void
+                     */
+                    function caller($callback) {}
+
+                    /**
+                     * @param string $a
+                     * @return void
+                     */
+                    function foo($a) {}
+
+                    caller("foo");',
+                'error_message' => 'InvalidScalarArgument',
+            ],
+            'callableArgsCountMismatch' => [
+                '<?php
+                    /**
+                     * @param callable(string):void $callback
+                     * @return void
+                     */
+                    function caller($callback) {}
+
+                    /**
+                     * @param string $a
+                     * @param string $b
+                     * @return void
+                     */
+                    function foo($a, $b) {}
+
+                    caller("foo");',
+                'error_message' => 'InvalidScalarArgument',
+            ],
         ];
     }
 }
diff --git a/tests/Template/FunctionTemplateTest.php b/tests/Template/FunctionTemplateTest.php
index 407e96ebe5c..70b99124934 100644
--- a/tests/Template/FunctionTemplateTest.php
+++ b/tests/Template/FunctionTemplateTest.php
@@ -1560,13 +1560,13 @@ function deserialize_object(string $data, string $type) {}'
                      * @template TNewKey of array-key
                      * @template TNewValue
                      * @psalm-param iterable<TKey, TValue> $iterable
-                     * @psalm-param callable(TKey, TValue): iterable<TNewKey, TNewValue> $mapper
+                     * @psalm-param callable(TKey): iterable<TNewKey, TNewValue> $mapper
                      * @psalm-return \Generator<TNewKey, TNewValue>
                      */
                     function map(iterable $iterable, callable $mapper): Generator
                     {
-                        foreach ($iterable as $key => $value) {
-                            yield from $mapper($key, $value);
+                        foreach ($iterable as $key => $_) {
+                            yield from $mapper($key);
                         }
                     }