diff --git a/Makefile.am b/Makefile.am
index eb249792d..34e152871 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -29,7 +29,8 @@ include/serno.h:
 			echo '#define SERNO "'$$revh'"' >include/serno.h ; \
 			echo "#define DATECODE $${datecode}UL" >>include/serno.h; \
 		fi \
-	else \
+	fi
+	@if [ ! -f include/serno.h ]; then \
 		echo '#define SERNO "unknown"' >include/serno.h; \
 		echo '#define DATECODE 0UL' >>include/serno.h; \
 	fi
diff --git a/librb/Makefile.am b/librb/Makefile.am
index 2cfeb8e2b..a21a3026f 100644
--- a/librb/Makefile.am
+++ b/librb/Makefile.am
@@ -9,4 +9,10 @@ BUILT_SOURCES = include/serno.h
 
 # NOTE: you'll want to change the below if you are unbundling
 include/serno.h:
-	@cp ../include/serno.h include/
+	@if [ -f ../include/serno.h ]; then \
+		cp ../include/serno.h include/; \
+	else \
+		echo '#define SERNO "unknown"' >include/serno.h; \
+		echo '#define DATECODE 0UL' >>include/serno.h; \
+	fi
+