diff --git a/bin/php-openapi b/bin/php-openapi
index 6f958da..b5f36ad 100755
--- a/bin/php-openapi
+++ b/bin/php-openapi
@@ -231,6 +231,9 @@ function read_input($inputFile, $inputFormat)
     } catch (Symfony\Component\Yaml\Exception\ParseException $e) {
         error($e->getMessage());
         exit(1);
+    } catch (cebe\openapi\exceptions\IOException $e) {
+        error($e->getMessage());
+        exit(1);
     }
     return $openApi;
 }
diff --git a/src/Reader.php b/src/Reader.php
index a2900d1..08c2996 100644
--- a/src/Reader.php
+++ b/src/Reader.php
@@ -7,6 +7,7 @@
 
 namespace cebe\openapi;
 
+use cebe\openapi\exceptions\IOException;
 use cebe\openapi\exceptions\TypeErrorException;
 use cebe\openapi\exceptions\UnresolvableReferenceException;
 use cebe\openapi\spec\OpenApi;
@@ -63,10 +64,17 @@ public static function readFromYaml(string $yaml, string $baseType = OpenApi::cl
      * The type of the returned object depends on the `$baseType` argument.
      * @throws TypeErrorException in case invalid spec data is supplied.
      * @throws UnresolvableReferenceException in case references could not be resolved.
+     * @throws IOException when the file is not readable.
      */
     public static function readFromJsonFile(string $fileName, string $baseType = OpenApi::class, $resolveReferences = true): SpecObjectInterface
     {
-        $spec = static::readFromJson(file_get_contents($fileName), $baseType);
+        $fileContent = file_get_contents($fileName);
+        if ($fileContent === false) {
+            $e = new IOException("Failed to read file: '$fileName'");
+            $e->fileName = $fileName;
+            throw $e;
+        }
+        $spec = static::readFromJson($fileContent, $baseType);
         $spec->setReferenceContext(new ReferenceContext($spec, $fileName));
         if ($resolveReferences) {
             $spec->resolveReferences();
@@ -89,10 +97,17 @@ public static function readFromJsonFile(string $fileName, string $baseType = Ope
      * The type of the returned object depends on the `$baseType` argument.
      * @throws TypeErrorException in case invalid spec data is supplied.
      * @throws UnresolvableReferenceException in case references could not be resolved.
+     * @throws IOException when the file is not readable.
      */
     public static function readFromYamlFile(string $fileName, string $baseType = OpenApi::class, $resolveReferences = true): SpecObjectInterface
     {
-        $spec = static::readFromYaml(file_get_contents($fileName), $baseType);
+        $fileContent = file_get_contents($fileName);
+        if ($fileContent === false) {
+            $e = new IOException("Failed to read file: '$fileName'");
+            $e->fileName = $fileName;
+            throw $e;
+        }
+        $spec = static::readFromYaml($fileContent, $baseType);
         $spec->setReferenceContext(new ReferenceContext($spec, $fileName));
         if ($resolveReferences) {
             $spec->resolveReferences();
diff --git a/src/Writer.php b/src/Writer.php
index 7388f4b..aecb213 100644
--- a/src/Writer.php
+++ b/src/Writer.php
@@ -7,6 +7,7 @@
 
 namespace cebe\openapi;
 
+use cebe\openapi\exceptions\IOException;
 use cebe\openapi\spec\OpenApi;
 use Symfony\Component\Yaml\Yaml;
 
@@ -40,19 +41,25 @@ public static function writeToYaml(SpecObjectInterface $object): string
      * Write OpenAPI spec object to JSON file.
      * @param SpecObjectInterface|OpenApi the OpenApi object instance.
      * @param string $fileName file name to write to.
+     * @throws IOException when writing the file fails.
      */
     public static function writeToJsonFile(SpecObjectInterface $object, string $fileName): void
     {
-        file_put_contents($fileName, static::writeToJson($object));
+        if (file_put_contents($fileName, static::writeToJson($object)) === false) {
+            throw new IOException("Failed to write file: '$fileName'");
+        }
     }
 
     /**
      * Write OpenAPI spec object to YAML file.
      * @param SpecObjectInterface|OpenApi the OpenApi object instance.
      * @param string $fileName file name to write to.
+     * @throws IOException when writing the file fails.
      */
     public static function writeToYamlFile(SpecObjectInterface $object, string $fileName): void
     {
-        file_put_contents($fileName, static::writeToYaml($object));
+        if (file_put_contents($fileName, static::writeToYaml($object)) === false) {
+            throw new IOException("Failed to write file: '$fileName'");
+        }
     }
 }
diff --git a/src/exceptions/IOException.php b/src/exceptions/IOException.php
new file mode 100644
index 0000000..1a68602
--- /dev/null
+++ b/src/exceptions/IOException.php
@@ -0,0 +1,20 @@
+<?php
+
+/**
+ * @copyright Copyright (c) 2018 Carsten Brandt <mail@cebe.cc> and contributors
+ * @license https://github.com/cebe/php-openapi/blob/master/LICENSE
+ */
+
+namespace cebe\openapi\exceptions;
+
+/**
+ * This exception is thrown when reading or writing of a file fails.
+ * @since 1.2.1
+ */
+class IOException extends \Exception
+{
+    /**
+     * @var string|null if available, the name of the affected file.
+     */
+    public $fileName;
+}
diff --git a/src/spec/Reference.php b/src/spec/Reference.php
index c28c303..bbc81a4 100644
--- a/src/spec/Reference.php
+++ b/src/spec/Reference.php
@@ -8,6 +8,7 @@
 namespace cebe\openapi\spec;
 
 use cebe\openapi\DocumentContextInterface;
+use cebe\openapi\exceptions\IOException;
 use cebe\openapi\exceptions\TypeErrorException;
 use cebe\openapi\exceptions\UnresolvableReferenceException;
 use cebe\openapi\json\InvalidJsonPointerSyntaxException;
@@ -156,6 +157,12 @@ public function resolve(ReferenceContext $context = null)
             }
         }
         $jsonReference = $this->_jsonReference;
+        if ($jsonReference === null) {
+            if ($context->throwException) {
+                throw new UnresolvableReferenceException(implode("\n", $this->getErrors()));
+            }
+            return $this;
+        }
         try {
             if ($jsonReference->getDocumentUri() === '') {
                 // resolve in current document
@@ -204,6 +211,14 @@ public function resolve(ReferenceContext $context = null)
             $this->_errors[] = $message;
             $this->_jsonReference = null;
             return $this;
+        } catch (UnresolvableReferenceException $e) {
+            $e->context = $this->getDocumentPosition();
+            if ($context->throwException) {
+                throw $e;
+            }
+            $this->_errors[] = $e->getMessage();
+            $this->_jsonReference = null;
+            return $this;
         }
     }
 
@@ -214,6 +229,11 @@ private function fetchReferencedFile($uri)
     {
         try {
             $content = file_get_contents($uri);
+            if ($content === false) {
+                $e = new IOException("Failed to read file: '$uri'");
+                $e->fileName = $uri;
+                throw $e;
+            }
             // TODO lazy content detection, should probably be improved
             if (strpos(ltrim($content), '{') === 0) {
                 return json_decode($content, true);