diff --git a/tests/actions.at b/tests/actions.at
index 84dab3c0..ea12d0e7 100644
--- a/tests/actions.at
+++ b/tests/actions.at
@@ -425,6 +425,7 @@ AT_DATA_GRAMMAR([[input.y]],
 ]$3[
 %code
 {
+#include <stdio.h> /* putchar. */
 ]AT_YYERROR_DECLARE[
 ]AT_YYLEX_DECLARE[
 }
@@ -1728,6 +1729,7 @@ AT_DATA_GRAMMAR([[input.y]],
 # define YYSTYPE sem_type
 
 ]AT_CXX_IF([[
+# include <cstdio> // EOF.
 # include <iostream>
   namespace
   {
diff --git a/tests/c++.at b/tests/c++.at
index 2224c7b7..be9fa10a 100644
--- a/tests/c++.at
+++ b/tests/c++.at
@@ -988,7 +988,8 @@ yy::parser::error (const std::string &m)
 
 # Another file to check syntax_error's linkage.
 AT_DATA_SOURCE([scan.cc],
-[[#include "input.hh"
+[[#include <cstdio>  // getchar
+#include "input.hh"
 
 // 'a': valid item, 's': syntax error, 'l': lexical error.
 int
diff --git a/tests/headers.at b/tests/headers.at
index 8b19d3fe..fa3556ac 100644
--- a/tests/headers.at
+++ b/tests/headers.at
@@ -127,6 +127,7 @@ AT_DATA_GRAMMAR([input.y],
 %define parse.error verbose
 ]AT_VARIANT_IF([%token <int> 'x'], [%union {int integer;}])[
 %code {
+#include <stdio.h> /* printf. */
 ]AT_PUSH_IF([[
 #if defined __GNUC__ && 7 == __GNUC__
 # pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
@@ -212,6 +213,7 @@ $2
   int integer;
 }
 %{
+#include <stdio.h> /* printf. */
 ]AT_PUSH_IF([[
 #if defined __GNUC__ && 7 == __GNUC__
 # pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
diff --git a/tests/regression.at b/tests/regression.at
index 1f308e90..9bfaf67b 100644
--- a/tests/regression.at
+++ b/tests/regression.at
@@ -1309,6 +1309,7 @@ AT_BISON_OPTION_PUSHDEFS([%debug $1])
 
 AT_DATA_GRAMMAR([input.y],
 [[%code {
+#include <stdio.h> /* printf */
   ]AT_YYERROR_DECLARE[
   ]AT_YYLEX_DECLARE[
 }
@@ -1480,12 +1481,13 @@ AT_DATA_GRAMMAR([input.y],
 }
 
 %{
+#include <stdio.h> /* printf. */
   ]AT_YYERROR_DECLARE[
   ]AT_YYLEX_DECLARE[
 %}
 
 %%
-exp: 'a' { fprintf (stdout, "x: %d, y: %d\n", x, y); };
+exp: 'a' { printf ("x: %d, y: %d\n", x, y); };
 %%
 ]AT_YYERROR_DEFINE[
 ]AT_YYLEX_DEFINE(["a"])[