diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index d4f851f8a..3ad34a619 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -338,12 +338,22 @@ class JsonFile
         $result = $parser->lint($json);
         if (null === $result) {
             if (defined('JSON_ERROR_UTF8') && JSON_ERROR_UTF8 === json_last_error()) {
-                throw new \UnexpectedValueException('"'.$file.'" is not UTF-8, could not parse as JSON');
+                if ($file === null) {
+                    throw new \UnexpectedValueException('The input is not UTF-8, could not parse as JSON');
+                } else {
+                    throw new \UnexpectedValueException('"' . $file . '" is not UTF-8, could not parse as JSON');
+                }
             }
 
             return true;
         }
 
-        throw new ParsingException('"'.$file.'" does not contain valid JSON'."\n".$result->getMessage(), $result->getDetails());
+        if ($file === null) {
+            throw new ParsingException('The input does not contain valid JSON' . "\n" . $result->getMessage(),
+                $result->getDetails());
+        } else {
+            throw new ParsingException('"' . $file . '" does not contain valid JSON' . "\n" . $result->getMessage(),
+                $result->getDetails());
+        }
     }
 }