diff --git a/eclair/external_sources.ecl b/eclair/external_sources.ecl
index f82582a..4089025 100644
--- a/eclair/external_sources.ecl
+++ b/eclair/external_sources.ecl
@@ -11,3 +11,6 @@
 -file_tag+={external, "^trusted-firmware-m/platform/ext/cmsis/.*$"}
 -file_tag+={external, "^trusted-firmware-m/lib/ext/mbedcrypto/.*$"}
 
+# Ignore any auto-generated source files in build dir.
+-file_tag+={external, "^trusted-firmware-m/build/.*$"}
+