diff --git a/CloudObjects/SDK/Exceptions/CoreAPIException.php b/CloudObjects/SDK/Exceptions/CoreAPIException.php
index 50d0859..94fdbf2 100644
--- a/CloudObjects/SDK/Exceptions/CoreAPIException.php
+++ b/CloudObjects/SDK/Exceptions/CoreAPIException.php
@@ -11,4 +11,12 @@ namespace CloudObjects\SDK\Exceptions;
  */
 class CoreAPIException extends SDKException {
 
+	/**
+	 * @param string $message The error message.
+	 * @param \Throwable|null $previous The original exception that caused this error, if any.
+	 */
+	public function __construct(string $message = "", ?\Throwable $previous = null) {
+		parent::__construct($message, 0, $previous);
+	}
+
 }
diff --git a/CloudObjects/SDK/ObjectRetriever.php b/CloudObjects/SDK/ObjectRetriever.php
index f39f385..fb622b0 100644
--- a/CloudObjects/SDK/ObjectRetriever.php
+++ b/CloudObjects/SDK/ObjectRetriever.php
@@ -283,11 +283,24 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 				$this->putIntoCache($uriString, $object, $this->options['cache_ttl']);
 				$this->logInfoWithTime('Fetched <'.$uriString.'> from Core API ['.$response->getStatusCode().'].', $ts);
 			} catch (RequestException $e) {
-				if ($e->hasResponse())
-					$this->logInfoWithTime('Object <'.$uriString.'> not found in Core API ['.$e->getResponse()->getStatusCode().'].', $ts);
-				else
-					$this->logInfoWithTime('Object <'.$uriString.'> could not be retrieved from Core API.', $ts);
-				return null;
+				if ($e->hasResponse() && $e->getResponse()->getStatusCode() == 404) {
+					// not found
+					$this->logInfoWithTime('Object <'.$uriString.'> not found in Core API.', $ts);
+					return null;
+				} else
+				if ($e->hasResponse()) {
+					// other API error
+					$this->logInfoWithTime('Object <'.$uriString.'> could not be retrieved from Core API ['.$e->getResponse()->getStatusCode().'].', $ts);
+					throw new CoreAPIException($e->getMessage(), $e);
+				} else {
+					// API error without response					
+					$this->logInfoWithTime('Object <'.$uriString.'> could not be retrieved from Core API (no status code).', $ts);
+					throw new CoreAPIException($e->getMessage(), $e);
+				}					
+			} catch (Exception $e) {
+				// other exceptions
+				$this->logInfoWithTime('Object <'.$uriString.'> could not be retrieved from Core API (unexpected exception).', $ts);
+				throw new CoreAPIException($e->getMessage(), $e);
 			}
 		}
 
@@ -337,7 +350,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 
 			$this->logInfoWithTime('Fetched all objects with <'.$type.'> for <'.$namespaceCoid->getHost().'> from Core API ['.$response->getStatusCode().'].', $ts);
 		} catch (Exception $e) {
-			throw new CoreAPIException;
+			throw new CoreAPIException($e->getMessage(), $e);
 		}
 	
 		return $allIris;
@@ -379,7 +392,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 			$this->logInfoWithTime('Fetched all objects for <'.$namespaceCoid->getHost().'> from Core API ['.$response->getStatusCode().'].', $ts);
 
 		} catch (Exception $e) {
-			throw new CoreAPIException;
+			throw new CoreAPIException($e->getMessage(), $e);
 		}
 	
 		return $allIris;
@@ -413,7 +426,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 			$this->logInfoWithTime('Fetched object list for <'.$namespaceCoid->getHost().'> from Core API ['.$response->getStatusCode().'].', $ts);
 
 		} catch (Exception $e) {
-			throw new CoreAPIException;
+			throw new CoreAPIException($e->getMessage(), $e);
 		}
 
 		return $allIris;
@@ -452,7 +465,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 			$this->logInfoWithTime('Fetched object list with <'.$type.'> for <'.$namespaceCoid->getHost().'> from Core API ['.$response->getStatusCode().'].', $ts);
 
 		} catch (Exception $e) {
-			throw new CoreAPIException;
+			throw new CoreAPIException($e->getMessage(), $e);
 		}
 
 		return $allIris;
diff --git a/tests/OfflineTests/ObjectRetrieverMockTest.php b/tests/OfflineTests/ObjectRetrieverMockTest.php
index 034a304..6e88d70 100644
--- a/tests/OfflineTests/ObjectRetrieverMockTest.php
+++ b/tests/OfflineTests/ObjectRetrieverMockTest.php
@@ -9,6 +9,7 @@ namespace CloudObjects\SDK;
 use ML\IRI\IRI;
 use GuzzleHttp\Client, GuzzleHttp\Handler\MockHandler,
     GuzzleHttp\HandlerStack, GuzzleHttp\Psr7\Response;
+use CloudObjects\SDK\Exceptions\CoreAPIException;
 
 class ObjectRetrieverMockTest extends \PHPUnit\Framework\TestCase {
 
@@ -50,4 +51,23 @@ class ObjectRetrieverMockTest extends \PHPUnit\Framework\TestCase {
         $this->assertNull($object->getString('urn:example:nonexistingvalue'));
     }
 
+    public function testGetNonExistingResource() {
+        $this->setMockResponse(new Response(404));
+
+        // should return "null"        
+        $coid = new IRI('coid://nonexistingresource.example.com');
+
+        $object = $this->retriever->getObjectNode($coid);
+        $this->assertNull($object);
+    }
+
+    public function testWhenAPIThrowsError() {
+        $this->setMockResponse(new Response(500));
+
+        $coid = new IRI('coid://nonexistingresource.example.com');
+
+        $this->expectException(CoreAPIException::class);
+        $this->retriever->getObjectNode($coid);
+    }
+
 }