diff --git a/backend/analyze.go b/backend/analyze.go
index 38f8ef5..3a50833 100644
--- a/backend/analyze.go
+++ b/backend/analyze.go
@@ -385,6 +385,9 @@
 	// the file (only comments and whitespace can precede it).
 	libraryRegexp = regexp.MustCompile(`` +
 		`^(?:\s*//[^\n]*\n)*\s*` +
+		// TODO(fxbug.dev/70247): Remove the next two lines.
+		`(?:deprecated_syntax\s*;)?` +
+		`(?:\s*//[^\n]*\n)*\s*` +
 		`library\s+(` +
 		fidlIdentifierPattern +
 		`(?:\.` + fidlIdentifierPattern + `)*` +