diff --git a/internal/config/config.go b/internal/config/config.go
index 7a074be5e..2395211e2 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -63,7 +63,7 @@ type Settings struct {
 func defaultConfig(dataDir, configFile string) *Config {
 	forcePrepend := forcePrependDefault
 	forcePrependEnv := os.Getenv("ASDF_FORCE_PREPEND")
-	if forcePrependEnv == "yes" || (forcePrependEnv == "" && runtime.GOOS == "darwin") {
+	if strings.ToLower(forcePrependEnv) == "yes" || (forcePrependEnv == "" && runtime.GOOS == "darwin") {
 		forcePrepend = true
 	}
 	return &Config{
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 56d55ae7f..cb4db5062 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -33,6 +33,14 @@ func TestLoadConfigEnv_WithForcePrependEnv(t *testing.T) {
 		assert.True(t, config.ForcePrepend, "Then ForcePrepend property is true")
 	})
 
+	t.Run("When ASDF_FORCE_PREPEND env given YES", func(t *testing.T) {
+		t.Setenv("ASDF_FORCE_PREPEND", "YES")
+
+		config, _ := loadConfigEnv()
+
+		assert.True(t, config.ForcePrepend, "Then ForcePrepend property is true")
+	})
+
 	t.Run("When ASDF_FORCE_PREPEND env given any string other than yes", func(t *testing.T) {
 		t.Setenv("ASDF_FORCE_PREPEND", "no")