diff --git a/src/JsonSchema/ConstraintError.php b/src/JsonSchema/ConstraintError.php
index 0934292c3..0268dd4cd 100644
--- a/src/JsonSchema/ConstraintError.php
+++ b/src/JsonSchema/ConstraintError.php
@@ -54,6 +54,7 @@ class ConstraintError extends Enum
     public const NOT = 'not';
     public const ONE_OF = 'oneOf';
     public const REQUIRED = 'required';
+    public const UNRESOLVABLE_REF = 'unresolvableRef';
     public const REQUIRES = 'requires';
     public const PATTERN = 'pattern';
     public const PREGEX_INVALID = 'pregrex';
@@ -118,6 +119,7 @@ public function getMessage()
             self::NOT => 'Matched a schema which it should not',
             self::ONE_OF => 'Failed to match exactly one schema',
             self::REQUIRED => 'The property %s is required',
+            self::UNRESOLVABLE_REF => 'The $ref "%s" could not be resolved',
             self::REQUIRES => 'The presence of the property %s requires that %s also be present',
             self::PATTERN => 'Does not match the regex pattern %s',
             self::PREGEX_INVALID => 'The pattern %s is invalid',
diff --git a/src/JsonSchema/Constraints/Drafts/Draft06/RefConstraint.php b/src/JsonSchema/Constraints/Drafts/Draft06/RefConstraint.php
index f52bcda0a..e1e6c55f1 100644
--- a/src/JsonSchema/Constraints/Drafts/Draft06/RefConstraint.php
+++ b/src/JsonSchema/Constraints/Drafts/Draft06/RefConstraint.php
@@ -4,6 +4,7 @@
 
 namespace JsonSchema\Constraints\Drafts\Draft06;
 
+use JsonSchema\ConstraintError;
 use JsonSchema\Constraints\ConstraintInterface;
 use JsonSchema\Entity\ErrorBagProxy;
 use JsonSchema\Entity\JsonPointer;
@@ -30,6 +31,10 @@ public function check(&$value, $schema = null, ?JsonPointer $path = null, $i = n
         try {
             $refSchema = $this->factory->getSchemaStorage()->resolveRefSchema($schema);
         } catch (\Exception $e) {
+            // A $ref that cannot be resolved is a broken schema, not an absent keyword:
+            // returning here would let the value pass as if the $ref had not been written.
+            $this->addError(ConstraintError::UNRESOLVABLE_REF(), $path, ['ref' => $schema->{'$ref'}]);
+
             return;
         }
 
diff --git a/src/JsonSchema/Constraints/Drafts/Draft07/RefConstraint.php b/src/JsonSchema/Constraints/Drafts/Draft07/RefConstraint.php
index 9ec6efdac..9913d10e3 100644
--- a/src/JsonSchema/Constraints/Drafts/Draft07/RefConstraint.php
+++ b/src/JsonSchema/Constraints/Drafts/Draft07/RefConstraint.php
@@ -4,6 +4,7 @@
 
 namespace JsonSchema\Constraints\Drafts\Draft07;
 
+use JsonSchema\ConstraintError;
 use JsonSchema\Constraints\ConstraintInterface;
 use JsonSchema\Entity\ErrorBagProxy;
 use JsonSchema\Entity\JsonPointer;
@@ -30,6 +31,10 @@ public function check(&$value, $schema = null, ?JsonPointer $path = null, $i = n
         try {
             $refSchema = $this->factory->getSchemaStorage()->resolveRefSchema($schema);
         } catch (\Exception $e) {
+            // A $ref that cannot be resolved is a broken schema, not an absent keyword:
+            // returning here would let the value pass as if the $ref had not been written.
+            $this->addError(ConstraintError::UNRESOLVABLE_REF(), $path, ['ref' => $schema->{'$ref'}]);
+
             return;
         }
 
diff --git a/src/JsonSchema/Constraints/Drafts/Draft2019/RefConstraint.php b/src/JsonSchema/Constraints/Drafts/Draft2019/RefConstraint.php
index 989b1f039..a095234c0 100644
--- a/src/JsonSchema/Constraints/Drafts/Draft2019/RefConstraint.php
+++ b/src/JsonSchema/Constraints/Drafts/Draft2019/RefConstraint.php
@@ -4,6 +4,7 @@
 
 namespace JsonSchema\Constraints\Drafts\Draft2019;
 
+use JsonSchema\ConstraintError;
 use JsonSchema\Constraints\ConstraintInterface;
 use JsonSchema\Entity\ErrorBagProxy;
 use JsonSchema\Entity\JsonPointer;
@@ -30,6 +31,10 @@ public function check(&$value, $schema = null, ?JsonPointer $path = null, $i = n
         try {
             $refSchema = $this->factory->getSchemaStorage()->resolveRefSchema($schema);
         } catch (\Exception $e) {
+            // A $ref that cannot be resolved is a broken schema, not an absent keyword:
+            // returning here would let the value pass as if the $ref had not been written.
+            $this->addError(ConstraintError::UNRESOLVABLE_REF(), $path, ['ref' => $schema->{'$ref'}]);
+
             return;
         }
 
diff --git a/tests/Constraints/Draft06/RefConstraintTest.php b/tests/Constraints/Draft06/RefConstraintTest.php
new file mode 100644
index 000000000..94ce3d6ee
--- /dev/null
+++ b/tests/Constraints/Draft06/RefConstraintTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace JsonSchema\Tests\Constraints\Draft06;
+
+use JsonSchema\Constraints\Constraint;
+use JsonSchema\Tests\Constraints\VeryBaseTestCase;
+use JsonSchema\Validator;
+
+class RefConstraintTest extends VeryBaseTestCase
+{
+    private const DIALECT = 'http://json-schema.org/draft-06/schema#';
+
+    public function testAnUnresolvableRefIsReportedInsteadOfSilentlyPassing(): void
+    {
+        $validator = new Validator();
+        $data = new \stdClass();
+        $schema = json_decode('{"$schema": "' . self::DIALECT . '", "$ref": "#/$defs/nonExistent"}');
+
+        $validator->validate($data, $schema, Constraint::CHECK_MODE_STRICT);
+
+        self::assertFalse($validator->isValid());
+        $errors = $validator->getErrors();
+        self::assertCount(1, $errors);
+        self::assertSame('unresolvableRef', $errors[0]['constraint']['name']);
+    }
+
+    public function testAResolvableRefStillValidates(): void
+    {
+        $validator = new Validator();
+        $data = json_decode('{"child": 1}');
+        $schema = json_decode(
+            '{"$schema": "' . self::DIALECT . '", "$defs": {"num": {"type": "integer"}},'
+            . ' "properties": {"child": {"$ref": "#/$defs/num"}}}'
+        );
+
+        $validator->validate($data, $schema, Constraint::CHECK_MODE_STRICT);
+
+        self::assertTrue($validator->isValid(), (string) json_encode($validator->getErrors()));
+    }
+}
diff --git a/tests/Constraints/Draft07/RefConstraintTest.php b/tests/Constraints/Draft07/RefConstraintTest.php
new file mode 100644
index 000000000..68c14c7b3
--- /dev/null
+++ b/tests/Constraints/Draft07/RefConstraintTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace JsonSchema\Tests\Constraints\Draft07;
+
+use JsonSchema\Constraints\Constraint;
+use JsonSchema\Tests\Constraints\VeryBaseTestCase;
+use JsonSchema\Validator;
+
+class RefConstraintTest extends VeryBaseTestCase
+{
+    private const DIALECT = 'http://json-schema.org/draft-07/schema#';
+
+    public function testAnUnresolvableRefIsReportedInsteadOfSilentlyPassing(): void
+    {
+        $validator = new Validator();
+        $data = new \stdClass();
+        $schema = json_decode('{"$schema": "' . self::DIALECT . '", "$ref": "#/$defs/nonExistent"}');
+
+        $validator->validate($data, $schema, Constraint::CHECK_MODE_STRICT);
+
+        self::assertFalse($validator->isValid());
+        $errors = $validator->getErrors();
+        self::assertCount(1, $errors);
+        self::assertSame('unresolvableRef', $errors[0]['constraint']['name']);
+    }
+
+    public function testAResolvableRefStillValidates(): void
+    {
+        $validator = new Validator();
+        $data = json_decode('{"child": 1}');
+        $schema = json_decode(
+            '{"$schema": "' . self::DIALECT . '", "$defs": {"num": {"type": "integer"}},'
+            . ' "properties": {"child": {"$ref": "#/$defs/num"}}}'
+        );
+
+        $validator->validate($data, $schema, Constraint::CHECK_MODE_STRICT);
+
+        self::assertTrue($validator->isValid(), (string) json_encode($validator->getErrors()));
+    }
+}
diff --git a/tests/Constraints/Draft2019/RefConstraintTest.php b/tests/Constraints/Draft2019/RefConstraintTest.php
new file mode 100644
index 000000000..9c1867fe4
--- /dev/null
+++ b/tests/Constraints/Draft2019/RefConstraintTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace JsonSchema\Tests\Constraints\Draft2019;
+
+use JsonSchema\Constraints\Constraint;
+use JsonSchema\Tests\Constraints\VeryBaseTestCase;
+use JsonSchema\Validator;
+
+class RefConstraintTest extends VeryBaseTestCase
+{
+    private const DIALECT = 'https://json-schema.org/draft/2019-09/schema';
+
+    public function testAnUnresolvableRefIsReportedInsteadOfSilentlyPassing(): void
+    {
+        $validator = new Validator();
+        $data = new \stdClass();
+        $schema = json_decode('{"$schema": "' . self::DIALECT . '", "$ref": "#/$defs/nonExistent"}');
+
+        $validator->validate($data, $schema, Constraint::CHECK_MODE_STRICT);
+
+        self::assertFalse($validator->isValid());
+        $errors = $validator->getErrors();
+        self::assertCount(1, $errors);
+        self::assertSame('unresolvableRef', $errors[0]['constraint']['name']);
+    }
+
+    public function testAResolvableRefStillValidates(): void
+    {
+        $validator = new Validator();
+        $data = json_decode('{"child": 1}');
+        $schema = json_decode(
+            '{"$schema": "' . self::DIALECT . '", "$defs": {"num": {"type": "integer"}},'
+            . ' "properties": {"child": {"$ref": "#/$defs/num"}}}'
+        );
+
+        $validator->validate($data, $schema, Constraint::CHECK_MODE_STRICT);
+
+        self::assertTrue($validator->isValid(), (string) json_encode($validator->getErrors()));
+    }
+}