diff --git a/library/math.m b/library/math.m
index 1edc3ec66..b2eee12b3 100644
--- a/library/math.m
+++ b/library/math.m
@@ -189,6 +189,8 @@
 
 :- pragma(c_code, "
 
+	#include <stdio.h>
+
 	/*
 	** Handle domain errors.
 	*/
diff --git a/library/require.m b/library/require.m
index 8ec252281..9a0233514 100644
--- a/library/require.m
+++ b/library/require.m
@@ -47,6 +47,8 @@ require(Goal, Message) :-
 
 /* error/1, from require.m */
 
+:- pragma(c_header_code, "#include <stdio.h>").
+
 :- pragma(c_code, error(Message::in), "
 	fflush(stdout);
 	fprintf(stderr, ""Software error: %s\\n"", Message);