diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 55a68810f23..cbb65f8921a 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -547,6 +547,52 @@ DefineType(List *names, List *parameters)
 					   NameListToString(analyzeName));
 #endif
 
+	/*
+	 * Print warnings if any of the type's I/O functions are marked volatile.
+	 * There is a general assumption that I/O functions are stable or
+	 * immutable; this allows us for example to mark record_in/record_out
+	 * stable rather than volatile.  Ideally we would throw errors not just
+	 * warnings here; but since this check is new as of 9.5, and since the
+	 * volatility marking might be just an error-of-omission and not a true
+	 * indication of how the function behaves, we'll let it pass as a warning
+	 * for now.
+	 */
+	if (inputOid && func_volatile(inputOid) == PROVOLATILE_VOLATILE)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("type input function %s should not be volatile",
+						NameListToString(inputName))));
+	if (outputOid && func_volatile(outputOid) == PROVOLATILE_VOLATILE)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("type output function %s should not be volatile",
+						NameListToString(outputName))));
+	if (receiveOid && func_volatile(receiveOid) == PROVOLATILE_VOLATILE)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("type receive function %s should not be volatile",
+						NameListToString(receiveName))));
+	if (sendOid && func_volatile(sendOid) == PROVOLATILE_VOLATILE)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("type send function %s should not be volatile",
+						NameListToString(sendName))));
+	if (typmodinOid && func_volatile(typmodinOid) == PROVOLATILE_VOLATILE)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("type modifier input function %s should not be volatile",
+						NameListToString(typmodinName))));
+	if (typmodoutOid && func_volatile(typmodoutOid) == PROVOLATILE_VOLATILE)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("type modifier output function %s should not be volatile",
+						NameListToString(typmodoutName))));
+
+	/*
+	 * OK, we're done checking, time to make the type.  We must assign the
+	 * array type OID ahead of calling TypeCreate, since the base type and
+	 * array type each refer to the other.
+	 */
 	array_oid = AssignTypeArrayOid();
 
 	/*
diff --git a/src/test/regress/expected/create_cast.out b/src/test/regress/expected/create_cast.out
index 56cd86e00bf..88f94a63b48 100644
--- a/src/test/regress/expected/create_cast.out
+++ b/src/test/regress/expected/create_cast.out
@@ -6,12 +6,12 @@ CREATE TYPE casttesttype;
 CREATE FUNCTION casttesttype_in(cstring)
    RETURNS casttesttype
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  return type casttesttype is only a shell
 CREATE FUNCTION casttesttype_out(casttesttype)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  argument type casttesttype is only a shell
 CREATE TYPE casttesttype (
    internallength = variable,
diff --git a/src/test/regress/expected/create_type.out b/src/test/regress/expected/create_type.out
index 6dfe9169854..35e8f5d6a25 100644
--- a/src/test/regress/expected/create_type.out
+++ b/src/test/regress/expected/create_type.out
@@ -41,22 +41,22 @@ CREATE TYPE text_w_default;
 CREATE FUNCTION int42_in(cstring)
    RETURNS int42
    AS 'int4in'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  return type int42 is only a shell
 CREATE FUNCTION int42_out(int42)
    RETURNS cstring
    AS 'int4out'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  argument type int42 is only a shell
 CREATE FUNCTION text_w_default_in(cstring)
    RETURNS text_w_default
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  return type text_w_default is only a shell
 CREATE FUNCTION text_w_default_out(text_w_default)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 NOTICE:  argument type text_w_default is only a shell
 CREATE TYPE int42 (
    internallength = 4,
diff --git a/src/test/regress/input/create_function_1.source b/src/test/regress/input/create_function_1.source
index 1fded846a05..f2b1561cc24 100644
--- a/src/test/regress/input/create_function_1.source
+++ b/src/test/regress/input/create_function_1.source
@@ -5,22 +5,22 @@
 CREATE FUNCTION widget_in(cstring)
    RETURNS widget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION widget_out(widget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION int44in(cstring)
    RETURNS city_budget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION int44out(city_budget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 
 CREATE FUNCTION check_primary_key ()
 	RETURNS trigger
diff --git a/src/test/regress/output/create_function_1.source b/src/test/regress/output/create_function_1.source
index 9926c9073e7..30c2936f8d1 100644
--- a/src/test/regress/output/create_function_1.source
+++ b/src/test/regress/output/create_function_1.source
@@ -4,24 +4,24 @@
 CREATE FUNCTION widget_in(cstring)
    RETURNS widget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  type "widget" is not yet defined
 DETAIL:  Creating a shell type definition.
 CREATE FUNCTION widget_out(widget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  argument type widget is only a shell
 CREATE FUNCTION int44in(cstring)
    RETURNS city_budget
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  type "city_budget" is not yet defined
 DETAIL:  Creating a shell type definition.
 CREATE FUNCTION int44out(city_budget)
    RETURNS cstring
    AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
+   LANGUAGE C STRICT IMMUTABLE;
 NOTICE:  argument type city_budget is only a shell
 CREATE FUNCTION check_primary_key ()
 	RETURNS trigger
diff --git a/src/test/regress/sql/create_cast.sql b/src/test/regress/sql/create_cast.sql
index ad348daa097..b11cf88b064 100644
--- a/src/test/regress/sql/create_cast.sql
+++ b/src/test/regress/sql/create_cast.sql
@@ -8,11 +8,11 @@ CREATE TYPE casttesttype;
 CREATE FUNCTION casttesttype_in(cstring)
    RETURNS casttesttype
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION casttesttype_out(casttesttype)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 
 CREATE TYPE casttesttype (
    internallength = variable,
diff --git a/src/test/regress/sql/create_type.sql b/src/test/regress/sql/create_type.sql
index a4906b64e10..96a075b0267 100644
--- a/src/test/regress/sql/create_type.sql
+++ b/src/test/regress/sql/create_type.sql
@@ -44,19 +44,19 @@ CREATE TYPE text_w_default;
 CREATE FUNCTION int42_in(cstring)
    RETURNS int42
    AS 'int4in'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION int42_out(int42)
    RETURNS cstring
    AS 'int4out'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION text_w_default_in(cstring)
    RETURNS text_w_default
    AS 'textin'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 CREATE FUNCTION text_w_default_out(text_w_default)
    RETURNS cstring
    AS 'textout'
-   LANGUAGE internal STRICT;
+   LANGUAGE internal STRICT IMMUTABLE;
 
 CREATE TYPE int42 (
    internallength = 4,