diff --git a/php/containers-schema.json b/php/containers-schema.json
index d82338c8..d039d205 100644
--- a/php/containers-schema.json
+++ b/php/containers-schema.json
@@ -14,7 +14,8 @@
 				"properties": {
 					"image": {
 						"type": "string",
-						"minLength": 1
+						"minLength": 1,
+						"pattern": "^[a-z0-9/-]+$"
 					},
 					"expose": {
 						"type": "array",