diff --git a/errgoengine.go b/errgoengine.go
index d55448c..dc8ed4a 100644
--- a/errgoengine.go
+++ b/errgoengine.go
@@ -39,7 +39,10 @@ func (e *ErrgoEngine) Analyze(workingPath, msg string) (*CompiledErrorTemplate,
 	// initial context data extraction
 	contextData := NewContextData(e.SharedStore, workingPath)
 	contextData.Analyzer = template.Language.AnalyzerFactory(contextData)
-	e.FS.FSs[1] = template.Language.stubFs
+
+	if template.Language.stubFs != nil {
+		e.FS.FSs[1] = template.Language.stubFs
+	}
 
 	groupNames := template.Pattern.SubexpNames()
 	for _, submatches := range template.Pattern.FindAllStringSubmatch(msg, -1) {
diff --git a/error_templates/test_utils/test_utils.go b/error_templates/test_utils/test_utils.go
index c8e6f4e..3a3b4d7 100644
--- a/error_templates/test_utils/test_utils.go
+++ b/error_templates/test_utils/test_utils.go
@@ -171,7 +171,7 @@ func (cases TestCases) Execute(t *testing.T) {
 				}
 
 				t.Run(caseName, func(t *testing.T) {
-					cases.engine.FS = tCase.Files
+					cases.engine.FS.FSs[0] = tCase.Files
 					template, data, err := cases.engine.Analyze("", tCase.Input)
 					if err != nil {
 						t.Fatal(err)