diff --git a/pkg/mod/mod.go b/pkg/mod/mod.go
index 8b8d60a..636018b 100644
--- a/pkg/mod/mod.go
+++ b/pkg/mod/mod.go
@@ -124,9 +124,15 @@ func (mf *File) AddComment(comment string) error {
 
 	return mf.flush()
 }
+
+// GoVersion returns a semver string containing the value of of the go directive.
+// For example, it will return "1.2.3" if the go.mod file contains the line "go 1.2.3".
+// If no go directive is found, it returns "1.0" because:
+// 1. "1.0" is a valid semver string, so it's always safe to parse this value using semver.MustParse().
+// 2. The semantics of the absence of a go directive in a go.mod file means all versions of Go should be able to compile it.
 func (mf *File) GoVersion() string {
 	if mf.m.Go == nil {
-		return ""
+		return "1.0"
 	}
 	return mf.m.Go.Version
 }
diff --git a/pkg/mod/mod_test.go b/pkg/mod/mod_test.go
index 4b15994..13e7bc5 100644
--- a/pkg/mod/mod_test.go
+++ b/pkg/mod/mod_test.go
@@ -43,7 +43,7 @@ func TestFile(t *testing.T) {
 		testutil.Equals(t, "", p)
 		testutil.Equals(t, "", comment)
 		testutil.Equals(t, []string(nil), mf.Comments())
-		testutil.Equals(t, "", mf.GoVersion())
+		testutil.Equals(t, "1.0", mf.GoVersion())
 		testutil.Equals(t, 0, len(mf.RequireDirectives()))
 		testutil.Equals(t, 0, len(mf.ReplaceDirectives()))
 		testutil.Equals(t, 0, len(mf.ExcludeDirectives()))