diff --git a/m4/nproc.m4 b/m4/nproc.m4
index fead234..abe785e 100644
--- a/m4/nproc.m4
+++ b/m4/nproc.m4
@@ -40,7 +40,8 @@ AC_DEFUN([gl_PREREQ_NPROC],
       [gl_cv_func_sched_getaffinity3],
       [AC_COMPILE_IFELSE(
          [AC_LANG_PROGRAM(
-            [[#include <sched.h>]],
+            [[#include <errno.h>
+              #include <sched.h>]],
             [[sched_getaffinity (0, 0, (cpu_set_t *) 0);]])],
          [gl_cv_func_sched_getaffinity3=yes],
          [gl_cv_func_sched_getaffinity3=no])
diff --git a/m4/sched_h.m4 b/m4/sched_h.m4
index f564541..7133747 100644
--- a/m4/sched_h.m4
+++ b/m4/sched_h.m4
@@ -10,6 +10,7 @@ AC_DEFUN([gl_SCHED_H],
 [
   AC_COMPILE_IFELSE(
     [AC_LANG_PROGRAM([[
+       #include <errno.h>
        #include <sched.h>
        struct sched_param a;
        int b[] = { SCHED_FIFO, SCHED_RR, SCHED_OTHER };
@@ -30,7 +31,8 @@ AC_DEFUN([gl_SCHED_H],
      if test "$HAVE_SCHED_H" = 1; then
        AC_CHECK_TYPE([struct sched_param],
          [HAVE_STRUCT_SCHED_PARAM=1], [HAVE_STRUCT_SCHED_PARAM=0],
-         [#include <sched.h>])
+         [#include <errno.h>
+          #include <sched.h>])
      else
        dnl On OS/2 kLIBC, struct sched_param is in spawn.h.
        AC_CHECK_TYPE([struct sched_param],
diff --git a/tests/test-sched.c b/tests/test-sched.c
index 52e0a8a..073fd04 100644
--- a/tests/test-sched.c
+++ b/tests/test-sched.c
@@ -18,6 +18,7 @@
 
 #include <config.h>
 
+#include <errno.h>
 #include <sched.h>
 
 /* Check that 'struct sched_param' is defined.  */