diff --git a/inst/schema/outpack/metadata.json b/inst/schema/outpack/metadata.json
index 85fd1272..7488e413 100644
--- a/inst/schema/outpack/metadata.json
+++ b/inst/schema/outpack/metadata.json
@@ -60,7 +60,7 @@
                 "properties": {
                     "path": {
                         "description": "The path of the file",
-                        "type": "string"
+                        "$ref": "relative-path.json"
                     },
                     "hash": {
                         "$ref": "hash.json"
@@ -88,17 +88,16 @@
                     },
                     "files": {
                         "type": "array",
-                        "minItems": 1,
                         "items": {
                             "type": "object",
                             "properties": {
                                 "here": {
                                     "description": "The path of the file in this packet",
-                                    "type": "string"
+                                    "$ref": "relative-path.json"
                                 },
                                 "there": {
                                     "description": "The path of the file within the upstream packet",
-                                    "type": "string"
+                                    "$ref": "relative-path.json"
                                 }
                             },
                             "required": ["here", "there"]
diff --git a/inst/schema/outpack/relative-path.json b/inst/schema/outpack/relative-path.json
new file mode 100644
index 00000000..1c27adee
--- /dev/null
+++ b/inst/schema/outpack/relative-path.json
@@ -0,0 +1,9 @@
+{
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "title": "File path",
+    "description": "A relative cross-platform file path",
+    "version": "0.1.1",
+
+    "type": "string",
+    "pattern": "^([^<>:\"/\\\\|?*\\x00-\\x1f]+/)*[^<>:\"/\\\\|?*\\x00-\\x1f]+$"
+}