diff --git a/src/Requests/Collections/CreateCollectionRequest.php b/src/Requests/Collections/CreateCollectionRequest.php
index 257797b..7497ce7 100644
--- a/src/Requests/Collections/CreateCollectionRequest.php
+++ b/src/Requests/Collections/CreateCollectionRequest.php
@@ -21,7 +21,7 @@ class CreateCollectionRequest extends Request implements HasBody
      */
     public function __construct(
         protected readonly string $name,
-        protected readonly int $size = 1536,
+        protected readonly ?int $size = null,
         protected readonly string $distance = 'Cosine',
         protected readonly ?array $namedVectors = null,
         protected readonly ?array $sparseVectors = null,
@@ -40,6 +40,13 @@ protected function defaultBody(): array
         if ($this->namedVectors !== null) {
             $body = ['vectors' => $this->namedVectors];
         } else {
+            if ($this->size === null) {
+                throw new \InvalidArgumentException(
+                    'Collection vector size is required: pass $size or $namedVectors. '
+                    .'A silent default dimension would have to match your embedding model by luck.'
+                );
+            }
+
             $body = [
                 'vectors' => [
                     'size' => $this->size,
diff --git a/tests/Unit/RequestTest.php b/tests/Unit/RequestTest.php
index 3e668f7..b81bf1d 100644
--- a/tests/Unit/RequestTest.php
+++ b/tests/Unit/RequestTest.php
@@ -398,11 +398,11 @@
 describe('CreateCollectionRequest with sparse vectors', function (): void {
     it('includes sparse_vectors in body', function (): void {
         $sparse = ['sparse' => ['modifier' => 'idf']];
-        $request = new CreateCollectionRequest('test', sparseVectors: $sparse);
+        $request = new CreateCollectionRequest('test', size: 1024, sparseVectors: $sparse);
         $body = invade($request)->defaultBody();
 
         expect($body['sparse_vectors'])->toBe($sparse)
-            ->and($body['vectors'])->toBe(['size' => 1536, 'distance' => 'Cosine']);
+            ->and($body['vectors'])->toBe(['size' => 1024, 'distance' => 'Cosine']);
     });
 
     it('combines named vectors with sparse vectors', function (): void {
@@ -416,11 +416,18 @@
     });
 
     it('omits sparse_vectors when null', function (): void {
-        $request = new CreateCollectionRequest('test');
+        $request = new CreateCollectionRequest('test', size: 1024);
         $body = invade($request)->defaultBody();
 
         expect($body)->not->toHaveKey('sparse_vectors');
     });
+
+    it('throws when neither size nor named vectors are given', function (): void {
+        $request = new CreateCollectionRequest('test');
+
+        expect(fn () => invade($request)->defaultBody())
+            ->toThrow(InvalidArgumentException::class, 'Collection vector size is required');
+    });
 });
 
 describe('AliasRequest', function (): void {