diff -up Linux-PAM-1.3.1/configure.ac.pam-misc-configurable Linux-PAM-1.3.1/configure.ac
--- Linux-PAM-1.3.1/configure.ac.pam-misc-configurable	2023-06-26 09:57:00.243146563 +0200
+++ Linux-PAM-1.3.1/configure.ac	2023-06-26 09:59:45.353636685 +0200
@@ -621,6 +621,13 @@ if test x"$opt_kerneloverflowuid" == x;
 fi
 AC_DEFINE_UNQUOTED(PAM_USERTYPE_OVERFLOW_UID, $opt_kerneloverflowuid, [Kernel overflow uid.])
 
+AC_ARG_WITH([misc-conv-bufsize],
+AS_HELP_STRING([--with-misc-conv-bufsize=<number>],
+    [Size of input buffer for libpam_misc's misc_conv() conversation function, default=4096]),
+    [],
+    [with_misc_conv_bufsize=4096])
+AC_DEFINE_UNQUOTED(PAM_MISC_CONV_BUFSIZE, $with_misc_conv_bufsize, [libpam_misc misc_conv() buffer size.])
+
 dnl Files to be created from when we run configure
 AC_CONFIG_FILES([Makefile libpam/Makefile libpamc/Makefile libpamc/test/Makefile \
 	libpam_misc/Makefile conf/Makefile conf/pam_conv1/Makefile \
diff -up Linux-PAM-1.3.1/libpam_misc/misc_conv.c.pam-misc-configurable Linux-PAM-1.3.1/libpam_misc/misc_conv.c
--- Linux-PAM-1.3.1/libpam_misc/misc_conv.c.pam-misc-configurable	2023-06-26 09:57:00.242146560 +0200
+++ Linux-PAM-1.3.1/libpam_misc/misc_conv.c	2023-06-26 10:00:38.023787972 +0200
@@ -18,7 +18,7 @@
 #include <security/pam_appl.h>
 #include <security/pam_misc.h>
 
-#define INPUTSIZE PAM_MAX_MSG_SIZE           /* maximum length of input+1 */
+#define INPUTSIZE PAM_MISC_CONV_BUFSIZE      /* maximum length of input+1 */
 #define CONV_ECHO_ON  1                            /* types of echo state */
 #define CONV_ECHO_OFF 0