.../EntityResource/EntityResourceTestBase.php        | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index cafb5d8..f2108ed 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -929,9 +929,17 @@ public function testPost() {
         // Some top-level keys in the normalization may not be fields on the
         // entity (for example '_links' and '_embedded' in the HAL normalization).
         if ($created_entity->hasField($field_name)) {
+          $field_type = $created_entity->get($field_name)->getFieldDefinition()->getType();
+          // Fields are stored in the database, when read they are represented
+          // as strings in PHP memory. The exception: field types that are
+          // stored in a serialized way. Hence we need to cast most expected
+          // field normalizations to strings.
+          $expected_field_normalization = $field_type !== 'map'
+            ? static::castToString($field_normalization)
+            : $field_normalization;
           // Subset, not same, because we can e.g. send just the target_id for the
           // bundle in a POST request; the response will include more properties.
-          $this->assertArraySubset(static::castToString($field_normalization), $created_entity->get($field_name)
+          $this->assertArraySubset($expected_field_normalization, $created_entity->get($field_name)
             ->getValue(), TRUE);
         }
       }
@@ -1190,9 +1198,17 @@ public function testPatch() {
       // Some top-level keys in the normalization may not be fields on the
       // entity (for example '_links' and '_embedded' in the HAL normalization).
       if ($updated_entity->hasField($field_name)) {
+        $field_type = $updated_entity->get($field_name)->getFieldDefinition()->getType();
+        // Fields are stored in the database, when read they are represented
+        // as strings in PHP memory. The exception: field types that are
+        // stored in a serialized way. Hence we need to cast most expected
+        // field normalizations to strings.
+        $expected_field_normalization = $field_type !== 'map'
+          ? static::castToString($field_normalization)
+          : $field_normalization;
         // Subset, not same, because we can e.g. send just the target_id for the
         // bundle in a PATCH request; the response will include more properties.
-        $this->assertArraySubset(static::castToString($field_normalization), $updated_entity->get($field_name)->getValue(), TRUE);
+        $this->assertArraySubset($expected_field_normalization, $updated_entity->get($field_name)->getValue(), TRUE);
       }
     }
     // Ensure that fields do not get deleted if they're not present in the PATCH