diff --git a/engine/resources/file.go b/engine/resources/file.go
index 95c8f783..02ec9ab6 100644
--- a/engine/resources/file.go
+++ b/engine/resources/file.go
@@ -327,6 +327,13 @@ func (obj *FileRes) Validate() error {
 		if !strings.HasPrefix(frag, "/") {
 			return fmt.Errorf("the frag (`%s`) isn't an absolute path", frag)
 		}
+		// If the file is inside one of our fragment dirs, then this
+		// would make an infinite loop mess. We can't prevent this
+		// happening in other ways with multiple dirs doing this for
+		// each other, but we can at least catch the common case.
+		if util.HasPathPrefix(obj.getPath(), frag) {
+			return fmt.Errorf("inside a frag (`%s`)", frag)
+		}
 	}
 
 	if obj.Purge && (isContent || isFrag) {
diff --git a/lang/interpret_test/TestAstFunc3/frag1.txtar b/lang/interpret_test/TestAstFunc3/frag1.txtar
new file mode 100644
index 00000000..8d1ff4af
--- /dev/null
+++ b/lang/interpret_test/TestAstFunc3/frag1.txtar
@@ -0,0 +1,16 @@
+-- main.mcl --
+file "/tmp/frags/" {
+	state => "exists",
+}
+file "/tmp/frags/f1" {
+	state => "exists",
+	content => "f1 contents\n",
+}
+file "/tmp/frags/all" {
+	state => "exists",
+	fragments => [
+		"/tmp/frags/",
+	],
+}
+-- OUTPUT --
+# err: errValidate: file[/tmp/frags/all] did not Validate: inside a frag (`/tmp/frags/`)