diff --git a/doc/build.py b/doc/build.py
index 31049716..7133c7b5 100755
--- a/doc/build.py
+++ b/doc/build.py
@@ -74,7 +74,7 @@ def build_docs(version='dev', **kwargs):
       GENERATE_MAN      = NO
       GENERATE_RTF      = NO
       CASE_SENSE_NAMES  = NO
-      INPUT             = {0}/core.h {0}/format.h {0}/ostream.h \
+      INPUT             = {0}/core.h {0}/format.h {0}/os.h {0}/ostream.h \
                           {0}/printf.h {0}/time.h
       QUIET             = YES
       JAVADOC_AUTOBRIEF = YES