diff --git a/validator/schema/platformsh.application.json b/validator/schema/platformsh.application.json
index 3cc6f70..fed7763 100644
--- a/validator/schema/platformsh.application.json
+++ b/validator/schema/platformsh.application.json
@@ -57,7 +57,11 @@
         "properties": {
           "source": {
             "type": "string",
-            "title": "The type of mount that will provide the data."
+            "title": "The type of mount that will provide the data.",
+            "enum": [
+              "local",
+              "service"
+            ]
           },
           "source_path": {
             "type": "string",
@@ -343,7 +347,11 @@
             "properties": {
               "source": {
                 "type": "string",
-                "title": "The type of mount that will provide the data."
+                "title": "The type of mount that will provide the data.",
+                "enum": [
+                  "local",
+                  "service"
+                ]
               },
               "source_path": {
                 "type": "string",
@@ -724,7 +732,11 @@
               "properties": {
                 "source": {
                   "type": "string",
-                  "title": "The type of mount that will provide the data."
+                  "title": "The type of mount that will provide the data.",
+                  "enum": [
+                    "local",
+                    "service"
+                  ]
                 },
                 "source_path": {
                   "type": "string",
diff --git a/validator/schema/upsun.json b/validator/schema/upsun.json
index c69d7f9..3c8f9e0 100644
--- a/validator/schema/upsun.json
+++ b/validator/schema/upsun.json
@@ -56,7 +56,11 @@
               "properties": {
                 "source": {
                   "type": "string",
-                  "title": "The type of mount that will provide the data."
+                  "title": "The type of mount that will provide the data.",
+                  "enum": [
+                    "storage",
+                    "service"
+                  ]
                 },
                 "source_path": {
                   "type": "string",
@@ -338,7 +342,11 @@
                   "properties": {
                     "source": {
                       "type": "string",
-                      "title": "The type of mount that will provide the data."
+                      "title": "The type of mount that will provide the data.",
+                      "enum": [
+                        "storage",
+                        "service"
+                      ]
                     },
                     "source_path": {
                       "type": "string",
@@ -715,7 +723,11 @@
                     "properties": {
                       "source": {
                         "type": "string",
-                        "title": "The type of mount that will provide the data."
+                        "title": "The type of mount that will provide the data.",
+                        "enum": [
+                          "storage",
+                          "service"
+                        ]
                       },
                       "source_path": {
                         "type": "string",