diff --git a/core/manifest/ConfigManifest.php b/core/manifest/ConfigManifest.php
index af04ae9e9..e9091bf6f 100644
--- a/core/manifest/ConfigManifest.php
+++ b/core/manifest/ConfigManifest.php
@@ -99,7 +99,7 @@ class SS_ConfigManifest {
 		}
 
 		// If we don't have a variantKeySpec (because we're forcing regen, or it just wasn't in the cache), generate it
-		if (false === $this->variantKeySpec) {
+		if (false === $this->phpConfigSources || false === $this->variantKeySpec) {
 			$this->regenerate($includeTests);
 		}
 
diff --git a/tests/core/manifest/ConfigManifestTest.php b/tests/core/manifest/ConfigManifestTest.php
index a1fac8424..5b14df254 100644
--- a/tests/core/manifest/ConfigManifestTest.php
+++ b/tests/core/manifest/ConfigManifestTest.php
@@ -152,6 +152,83 @@ class ConfigManifestTest extends SapphireTest {
 		$manifest->__construct(dirname(__FILE__).'/fixtures/configmanifest', false, false);
 	}
 
+	/**
+	 * Test cache regeneration if all or some of the cache files are missing
+	 *
+	 * 1. Test regeneration if all cache files are missing
+	 * 2. Test regeneration if 'variant_key_spec' cache file is missing
+	 * 3. Test regeneration if 'php_config_sources' cache file is missing
+	 */
+	public function testAutomaticCacheRegeneration(){
+		$base = dirname(__FILE__) . '/fixtures/configmanifest';
+
+		// Test regeneration if all cache files are missing
+		$manifest = $this->getManifestMock(array('getCache', 'regenerate', 'buildYamlConfigVariant'));
+
+		$manifest->expects($this->once())// regenerate should be called once
+			->method('regenerate')
+			->with($this->equalTo(false)); // includeTests = false
+
+		// Set up a cache where we expect load to never be called
+		$cache = $this->getCacheMock();
+		$cache->expects($this->exactly(2))
+			->will($this->returnValue(false))
+			->method('load');
+
+		$manifest->expects($this->any())
+			->method('getCache')
+			->will($this->returnValue($cache));
+
+		$manifest->__construct($base);
+
+		// Test regeneration if 'variant_key_spec' cache file is missing
+		$manifest = $this->getManifestMock(array('getCache', 'regenerate', 'buildYamlConfigVariant'));
+
+		$manifest->expects($this->once())// regenerate should be called once
+			->method('regenerate')
+			->with($this->equalTo(false)); // includeTests = false
+
+
+		$cache = $this->getCacheMock();
+		$cache->expects($this->exactly(2))
+			->method('load')
+			->will($this->returnCallback(function ($parameter) {
+				if (strpos($parameter, 'variant_key_spec') !== false) {
+					return false;
+				}
+				return array();
+			}));
+
+		$manifest->expects($this->any())
+			->method('getCache')
+			->will($this->returnValue($cache));
+
+		$manifest->__construct($base);
+
+		// Test regeneration if 'php_config_sources' cache file is missing
+		$manifest = $this->getManifestMock(array('getCache', 'regenerate', 'buildYamlConfigVariant'));
+
+		$manifest->expects($this->once())// regenerate should be called once
+			->method('regenerate')
+			->with($this->equalTo(false)); // includeTests = false
+
+		$cache = $this->getCacheMock();
+		$cache->expects($this->exactly(2))
+			->method('load')
+			->will($this->returnCallback(function ($parameter) {
+				if (strpos($parameter, 'php_config_sources') !== false) {
+					return false;
+				}
+				return array();
+			}));
+
+		$manifest->expects($this->any())
+			->method('getCache')
+			->will($this->returnValue($cache));
+
+		$manifest->__construct($base);
+	}
+
 	/**
 	 * This test checks the processing of before and after reference paths (module-name/filename#fragment)
 	 * This method uses fixture/configmanifest/mysite/_config/addyamlconfigfile.yml as a fixture