diff --git a/CHANGELOG.md b/CHANGELOG.md
index 912c327..8436d5b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,14 @@
 All notable changes to this project will be documented in this file. This project adheres to
 [Semantic Versioning](http://semver.org/) and [this changelog format](http://keepachangelog.com/).
 
+## Unreleased
+
+### Added
+
+- [#30](https://github.com/laravel-json-api/eloquent/pull/30) Allow a wider range of Eloquent relations in
+  the `QueryToMany` and `QueryToOne` classes. This means packages
+  like [culturegr/custom-relation](https://github.com/culturegr/custom-relation) will work with this package.
+
 ## [3.0.1] - 2023-04-03
 
 ### Fixed
diff --git a/src/QueryToMany.php b/src/QueryToMany.php
index 62b680b..f14dd57 100644
--- a/src/QueryToMany.php
+++ b/src/QueryToMany.php
@@ -20,10 +20,6 @@
 namespace LaravelJsonApi\Eloquent;
 
 use Illuminate\Database\Eloquent\Model;
-use Illuminate\Database\Eloquent\Relations\BelongsToMany as EloquentBelongsToMany;
-use Illuminate\Database\Eloquent\Relations\HasMany as EloquentHasMany;
-use Illuminate\Database\Eloquent\Relations\HasManyThrough as EloquentHasManyThrough;
-use Illuminate\Database\Eloquent\Relations\MorphMany as EloquentMorphMany;
 use Illuminate\Database\Eloquent\Relations\Relation as EloquentRelation;
 use Illuminate\Support\LazyCollection;
 use LaravelJsonApi\Contracts\Pagination\Page;
@@ -32,8 +28,6 @@
 use LaravelJsonApi\Core\Query\Custom\ExtendedQueryParameters;
 use LaravelJsonApi\Eloquent\Fields\Relations\ToMany;
 use LaravelJsonApi\Eloquent\QueryBuilder\JsonApiBuilder;
-use LogicException;
-use function get_class;
 use function sprintf;
 
 class QueryToMany implements QueryManyBuilder, HasPagination
@@ -165,30 +159,22 @@ public function query(): JsonApiBuilder
     private function getRelation(): EloquentRelation
     {
         $name = $this->relation->relationName();
-        $relation = $this->model->{$name}();
 
-        if ($relation instanceof EloquentHasMany ||
-            $relation instanceof EloquentBelongsToMany ||
-            $relation instanceof EloquentHasManyThrough ||
-            $relation instanceof EloquentMorphMany
-        ) {
-            return $relation;
-        }
+        assert(method_exists($this->model, $name), sprintf(
+            'Expecting method %s to exist on model %s',
+            $name,
+            $this->model::class,
+        ));
 
-        if ($relation instanceof EloquentRelation) {
-            throw new LogicException(sprintf(
-                'Eloquent relation %s on model %s returned a %s relation, which is not a to-many relation.',
-                $name,
-                get_class($this->model),
-                get_class($relation)
-            ));
-        }
+        $relation = $this->model->{$name}();
 
-        throw new LogicException(sprintf(
+        assert($relation instanceof EloquentRelation, sprintf(
             'Expecting method %s on model %s to return an Eloquent relation.',
             $name,
-            get_class($this->model)
+            $this->model::class,
         ));
+
+        return $relation;
     }
 
     /**
diff --git a/src/QueryToOne.php b/src/QueryToOne.php
index cd20c11..79d6a72 100644
--- a/src/QueryToOne.php
+++ b/src/QueryToOne.php
@@ -20,17 +20,12 @@
 namespace LaravelJsonApi\Eloquent;
 
 use Illuminate\Database\Eloquent\Model;
-use Illuminate\Database\Eloquent\Relations\BelongsTo as EloquentBelongsTo;
-use Illuminate\Database\Eloquent\Relations\HasOne as EloquentHasOne;
-use Illuminate\Database\Eloquent\Relations\HasOneThrough as EloquentHasOneThrough;
-use Illuminate\Database\Eloquent\Relations\MorphOne as EloquentMorphOne;
 use Illuminate\Database\Eloquent\Relations\Relation as EloquentRelation;
 use LaravelJsonApi\Contracts\Store\QueryOneBuilder;
 use LaravelJsonApi\Contracts\Store\QueryOneBuilder as QueryOneBuilderContract;
 use LaravelJsonApi\Core\Query\Custom\ExtendedQueryParameters;
 use LaravelJsonApi\Eloquent\Fields\Relations\ToOne;
 use LaravelJsonApi\Eloquent\QueryBuilder\JsonApiBuilder;
-use LogicException;
 use function sprintf;
 
 class QueryToOne implements QueryOneBuilder
@@ -103,30 +98,22 @@ public function query(): JsonApiBuilder
     private function getRelation(): EloquentRelation
     {
         $name = $this->relation->relationName();
-        $relation = $this->model->{$name}();
 
-        if ($relation instanceof EloquentHasOne ||
-            $relation instanceof EloquentBelongsTo ||
-            $relation instanceof EloquentHasOneThrough ||
-            $relation instanceof EloquentMorphOne
-        ) {
-            return $relation;
-        }
+        assert(method_exists($this->model, $name), sprintf(
+            'Expecting method %s to exist on model %s',
+            $name,
+            $this->model::class,
+        ));
 
-        if ($relation instanceof EloquentRelation) {
-            throw new LogicException(sprintf(
-                'Eloquent relation %s on model %s returned a %s relation, which is not a to-one relation.',
-                $name,
-                get_class($this->model),
-                get_class($relation)
-            ));
-        }
+        $relation = $this->model->{$name}();
 
-        throw new LogicException(sprintf(
+        assert($relation instanceof EloquentRelation, sprintf(
             'Expecting method %s on model %s to return an Eloquent relation.',
             $name,
-            get_class($this->model)
+            $this->model::class,
         ));
+
+        return $relation;
     }
 
     /**