diff --git a/src/backend/libpq/auth-sasl.c b/src/backend/libpq/auth-sasl.c
index 08b24d90b4..4039e7fa3e 100644
--- a/src/backend/libpq/auth-sasl.c
+++ b/src/backend/libpq/auth-sasl.c
@@ -20,14 +20,6 @@
 #include "libpq/pqformat.h"
 #include "libpq/sasl.h"
 
-/*
- * Maximum accepted size of SASL messages.
- *
- * The messages that the server or libpq generate are much smaller than this,
- * but have some headroom.
- */
-#define PG_MAX_SASL_MESSAGE_LENGTH	1024
-
 /*
  * Perform a SASL exchange with a libpq client, using a specific mechanism
  * implementation.
@@ -103,7 +95,7 @@ CheckSASLAuth(const pg_be_sasl_mech *mech, Port *port, char *shadow_pass,
 
 		/* Get the actual SASL message */
 		initStringInfo(&buf);
-		if (pq_getmessage(&buf, PG_MAX_SASL_MESSAGE_LENGTH))
+		if (pq_getmessage(&buf, mech->max_message_length))
 		{
 			/* EOF - pq_getmessage already logged error */
 			pfree(buf.data);
diff --git a/src/backend/libpq/auth-scram.c b/src/backend/libpq/auth-scram.c
index 03ddddc3c2..e4be4d499e 100644
--- a/src/backend/libpq/auth-scram.c
+++ b/src/backend/libpq/auth-scram.c
@@ -113,7 +113,9 @@ static int	scram_exchange(void *opaq, const char *input, int inputlen,
 const pg_be_sasl_mech pg_be_scram_mech = {
 	scram_get_mechanisms,
 	scram_init,
-	scram_exchange
+	scram_exchange,
+
+	PG_MAX_SASL_MESSAGE_LENGTH
 };
 
 /*
diff --git a/src/include/libpq/sasl.h b/src/include/libpq/sasl.h
index 7a1f970cca..3f2c02b8f2 100644
--- a/src/include/libpq/sasl.h
+++ b/src/include/libpq/sasl.h
@@ -26,6 +26,14 @@
 #define PG_SASL_EXCHANGE_SUCCESS		1
 #define PG_SASL_EXCHANGE_FAILURE		2
 
+/*
+ * Maximum accepted size of SASL messages.
+ *
+ * The messages that the server or libpq generate are much smaller than this,
+ * but have some headroom.
+ */
+#define PG_MAX_SASL_MESSAGE_LENGTH	1024
+
 /*
  * Backend SASL mechanism callbacks.
  *
@@ -127,6 +135,9 @@ typedef struct pg_be_sasl_mech
 							 const char *input, int inputlen,
 							 char **output, int *outputlen,
 							 const char **logdetail);
+
+	/* The maximum size allowed for client SASLResponses. */
+	int			max_message_length;
 } pg_be_sasl_mech;
 
 /* Common implementation for auth.c */