diff --git a/media/mtransport/build/moz.build b/media/mtransport/build/moz.build
index 5104355285dc..0deb9c394af0 100644
--- a/media/mtransport/build/moz.build
+++ b/media/mtransport/build/moz.build
@@ -26,6 +26,7 @@ EXPORTS.mtransport += [
 
 include('../objs.mozbuild')
 
+# These files cannot be built in unified mode because they force NSPR logging.
 SOURCES += mtransport_cppsrcs
 
 LIBRARY_NAME = 'mtransport'
diff --git a/media/mtransport/standalone/moz.build b/media/mtransport/standalone/moz.build
index 8fc2545e6f20..d287e07aba92 100644
--- a/media/mtransport/standalone/moz.build
+++ b/media/mtransport/standalone/moz.build
@@ -6,6 +6,7 @@
 
 include('../objs.mozbuild')
 
+# These files cannot be built in unified mode because they force NSPR logging.
 SOURCES += mtransport_cppsrcs
 
 LIBRARY_NAME = 'mtransport_s'