diff --git a/src/Composer/Package/Dumper/ArrayDumper.php b/src/Composer/Package/Dumper/ArrayDumper.php
index 6593143d5..b1e20dbf5 100644
--- a/src/Composer/Package/Dumper/ArrayDumper.php
+++ b/src/Composer/Package/Dumper/ArrayDumper.php
@@ -48,7 +48,9 @@ class ArrayDumper
         if ($package->getSourceType()) {
             $data['source']['type'] = $package->getSourceType();
             $data['source']['url'] = $package->getSourceUrl();
-            $data['source']['reference'] = $package->getSourceReference();
+            if (null !== ($value = $package->getSourceReference())) {
+                $data['source']['reference'] = $value;
+            }
             if ($mirrors = $package->getSourceMirrors()) {
                 $data['source']['mirrors'] = $mirrors;
             }
@@ -57,8 +59,12 @@ class ArrayDumper
         if ($package->getDistType()) {
             $data['dist']['type'] = $package->getDistType();
             $data['dist']['url'] = $package->getDistUrl();
-            $data['dist']['reference'] = $package->getDistReference();
-            $data['dist']['shasum'] = $package->getDistSha1Checksum();
+            if (null !== ($value = $package->getDistReference())) {
+                $data['dist']['reference'] = $value;
+            }
+            if (null !== ($value = $package->getDistSha1Checksum())) {
+                $data['dist']['shasum'] = $value;
+            }
             if ($mirrors = $package->getDistMirrors()) {
                 $data['dist']['mirrors'] = $mirrors;
             }
diff --git a/src/Composer/Package/Loader/ArrayLoader.php b/src/Composer/Package/Loader/ArrayLoader.php
index 303cc3c13..c269afa22 100644
--- a/src/Composer/Package/Loader/ArrayLoader.php
+++ b/src/Composer/Package/Loader/ArrayLoader.php
@@ -85,7 +85,7 @@ class ArrayLoader implements LoaderInterface
             }
             $package->setSourceType($config['source']['type']);
             $package->setSourceUrl($config['source']['url']);
-            $package->setSourceReference($config['source']['reference']);
+            $package->setSourceReference(isset($config['source']['reference']) ? $config['source']['reference'] : null);
             if (isset($config['source']['mirrors'])) {
                 $package->setSourceMirrors($config['source']['mirrors']);
             }