diff --git a/src/Expectation.php b/src/Expectation.php
index b229416a..a973c760 100644
--- a/src/Expectation.php
+++ b/src/Expectation.php
@@ -236,8 +236,8 @@ final class Expectation
     {
         $condition = is_callable($condition)
             ? $condition
-            : static function () use ($condition): mixed {
-                return $condition;
+            : static function () use ($condition): bool {
+                return (bool) $condition; // @phpstan-ignore-line
             };
 
         return $this->when(!$condition(), $callback);
@@ -253,8 +253,8 @@ final class Expectation
     {
         $condition = is_callable($condition)
             ? $condition
-            : static function () use ($condition): mixed {
-                return $condition;
+            : static function () use ($condition): bool {
+                return (bool) $condition; // @phpstan-ignore-line
             };
 
         if ($condition()) {
diff --git a/src/PendingObjects/TestCall.php b/src/PendingObjects/TestCall.php
index 287ca7a9..88928876 100644
--- a/src/PendingObjects/TestCall.php
+++ b/src/PendingObjects/TestCall.php
@@ -87,8 +87,8 @@ final class TestCall
     {
         $condition = is_callable($condition)
             ? $condition
-            : static function () use ($condition): mixed {
-                return $condition;
+            : static function () use ($condition): bool {
+                return (bool) $condition; // @phpstan-ignore-line
             };
 
         if ($condition()) {