diff --git a/msvc/gmp/config-vc6.gc b/msvc/gmp/config-vc6.gc
index f872ba06a..f53f7ae9a 100644
--- a/msvc/gmp/config-vc6.gc
+++ b/msvc/gmp/config-vc6.gc
@@ -375,7 +375,7 @@ MA 02111-1307, USA. */
 #define HAVE_STRING_H		1
 
 /* Define if you have the `strnlen' function. */
-#undef HAVE_STRNLEN
+#define HAVE_STRNLEN		1
 
 /* Define if you have the `strtoul' function. */
 #define HAVE_STRTOUL		1
diff --git a/msvc/gmp/config-vc6.p0 b/msvc/gmp/config-vc6.p0
index 9bfd9862a..035c98199 100644
--- a/msvc/gmp/config-vc6.p0
+++ b/msvc/gmp/config-vc6.p0
@@ -400,7 +400,7 @@ MA 02111-1307, USA. */
 #define HAVE_STRING_H		1
 
 /* Define if you have the `strnlen' function. */
-#undef HAVE_STRNLEN
+#define HAVE_STRNLEN		1
 
 /* Define if you have the `strtoul' function. */
 #define HAVE_STRTOUL		1
diff --git a/msvc/gmp/config-vc6.p3 b/msvc/gmp/config-vc6.p3
index f010e94d4..9c26cd32f 100644
--- a/msvc/gmp/config-vc6.p3
+++ b/msvc/gmp/config-vc6.p3
@@ -406,7 +406,7 @@ MA 02111-1307, USA. */
 #define HAVE_STRING_H		1
 
 /* Define if you have the `strnlen' function. */
-#undef HAVE_STRNLEN
+#define HAVE_STRNLEN		1
 
 /* Define if you have the `strtoul' function. */
 #define HAVE_STRTOUL		1
diff --git a/msvc/gmp/config-vc6.p4 b/msvc/gmp/config-vc6.p4
index b8f936977..180a5f4af 100644
--- a/msvc/gmp/config-vc6.p4
+++ b/msvc/gmp/config-vc6.p4
@@ -409,7 +409,7 @@ MA 02111-1307, USA. */
 #define HAVE_STRING_H		1
 
 /* Define if you have the `strnlen' function. */
-#undef HAVE_STRNLEN
+#define HAVE_STRNLEN		1
 
 /* Define if you have the `strtoul' function. */
 #define HAVE_STRTOUL		1