diff --git a/doc/bison.texi b/doc/bison.texi
index a559649c..77357813 100644
--- a/doc/bison.texi
+++ b/doc/bison.texi
@@ -2644,6 +2644,13 @@ calculator.
 
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+%code top {
+  /* Portability issues for strdup. */
+#ifndef _XOPEN_SOURCE
+# define _XOPEN_SOURCE 600
+#endif
+}
 @end example
 @end ignore
 
@@ -2875,7 +2882,7 @@ found, a pointer to that symbol is returned; otherwise zero is returned.
    not make these assumptions.  */
 #include <assert.h>
 #include <stdlib.h> /* malloc, realloc. */
-#include <string.h> /* strlen. */
+#include <string.h> /* strdup, strlen. */
 @end group
 
 @group
diff --git a/examples/c/bistromathic/parse.y b/examples/c/bistromathic/parse.y
index fbdeb7fc..5c1e6055 100644
--- a/examples/c/bistromathic/parse.y
+++ b/examples/c/bistromathic/parse.y
@@ -21,6 +21,11 @@
 
 // Emitted on top of the implementation file.
 %code top {
+  /* Portability issues for strdup. */
+  #ifndef _XOPEN_SOURCE
+  # define _XOPEN_SOURCE 600
+  #endif
+
   #include <ctype.h>  // isdigit
   #include <locale.h> // LC_ALL
   #include <math.h>   // cos, sin, etc.
diff --git a/examples/c/glr/c++-types.y b/examples/c/glr/c++-types.y
index 4c978386..ff1b62fb 100644
--- a/examples/c/glr/c++-types.y
+++ b/examples/c/glr/c++-types.y
@@ -53,6 +53,10 @@
 
 %code
 {
+  /* Portability issues for strdup. */
+#ifndef _XOPEN_SOURCE
+# define _XOPEN_SOURCE 600
+#endif
 
 #include <assert.h>
 #include <ctype.h>
diff --git a/tests/glr-regression.at b/tests/glr-regression.at
index a10f69ba..3a226f65 100644
--- a/tests/glr-regression.at
+++ b/tests/glr-regression.at
@@ -295,9 +295,7 @@ FILE *input;
     else
       {
         assert (strlen (buf) < sizeof buf - 1);
-        char *s = YY_CAST (char *, malloc (strlen (buf) + 1));
-        strcpy (s, buf);
-        ]AT_VAL[ = s;
+        ]AT_VAL[ = strdup (buf);
         return 'V';
       }
     break;
diff --git a/tests/testsuite.h b/tests/testsuite.h
index 46e99dfe..d2be5e62 100644
--- a/tests/testsuite.h
+++ b/tests/testsuite.h
@@ -10,3 +10,8 @@
 #  pragma GCC diagnostic ignored "-Wzero-as-null-pointer-constant"
 # endif
 #endif
+
+/* We use strdup, make it available.  */
+#ifndef _XOPEN_SOURCE
+# define _XOPEN_SOURCE 600
+#endif