diff --git a/sigmf-schema.json b/sigmf-schema.json
index c4ab916..ff2bc44 100644
--- a/sigmf-schema.json
+++ b/sigmf-schema.json
@@ -111,6 +111,7 @@
             "coordinates": {
               "type": "array",
               "minItems": 2,
+              "maxItems": 3,
               "items": {
                 "type": "number"
               }
@@ -214,6 +215,7 @@
                   "coordinates": {
                     "type": "array",
                     "minItems": 2,
+                    "maxItems": 3,
                     "items": {
                       "type": "number"
                     }