diff --git a/include/ac/string.h b/include/ac/string.h
index 744b4adabc..8cf7bf0e04 100644
--- a/include/ac/string.h
+++ b/include/ac/string.h
@@ -44,11 +44,11 @@
 
 #ifndef HAVE_STRDUP
 	/* strdup() is missing, declare our own version */
-	extern char *strdup( const char *s );
-#else
-	/* provide our own strdup */
 	extern char *ldap_pvt_strdup( const char * s );
 #	define strdup ldap_pvt_strdup
+#else
+	/* some systems fail to declare strdup */
+	extern char *strdup();
 #endif
 
 /*