Index: Mk/Uses/pgsql.mk
===================================================================
--- Mk/Uses/pgsql.mk
+++ Mk/Uses/pgsql.mk
@@ -60,12 +60,6 @@
 IGNORE=		will not allow setting both DEFAULT_PGSQL_VER and WITH_PGSQL_VER.  Use DEFAULT_VERSIONS=pgsql=9.6 instead
 .  endif
 
-# Setting/finding PostgreSQL version we want.
-PG_CONFIG?=	${LOCALBASE}/bin/pg_config
-.  if exists(${PG_CONFIG})
-_PGSQL_VER!=	${PG_CONFIG} --version | ${SED} -n 's/PostgreSQL[^0-9]*\([0-9]\.*[0-9]\).*/\1/p'
-.  endif
-
 # Handle the + and - version stuff
 .  if !empty(pgsql_ARGS)
 .    if ${pgsql_ARGS:M*+}
@@ -93,20 +87,20 @@
 .      endif
 PGSQL_VER?=	${version}
 .    endfor
-.    if defined(_PGSQL_VER)
-.      for v in ${_PGSQL_VER}
-.        if ${_WANT_PGSQL_VER:M$v} == ${_PGSQL_VER}
-PGSQL_VER=	${_PGSQL_VER}
+.    if defined(PGSQL_DEFAULT)
+.      for v in ${PGSQL_DEFAULT}
+.        if ${_WANT_PGSQL_VER:M$v} == ${PGSQL_DEFAULT}
+PGSQL_VER=	${PGSQL_DEFAULT}
 .        endif
 .      endfor
 .    endif
-.    if defined(_PGSQL_VER) && ${_PGSQL_VER} != ${PGSQL_VER}
-IGNORE?=	cannot install: the port wants postgresql-client version ${_WANT_PGSQL_VER} and you have version ${_PGSQL_VER} installed
+.    if defined(PGSQL_DEFAULT) && ${PGSQL_DEFAULT} != ${PGSQL_VER}
+IGNORE?=	cannot install: the port wants postgresql-client one of versions ${_WANT_PGSQL_VER:S/$/,/} but ${PGSQL_DEFAULT} is the default, or installed. To change the default version, add DEFAULT_VERSIONS+=pgsql=${PGSQL_VER} to your make.conf
 .    endif
 .  endif
 
 # OK, so the port is ambivalent, we'll just take what's on the system.
-PGSQL_VER?=	${_PGSQL_VER}
+PGSQL_VER?=	${PGSQL_DEFAULT}
 
 # After all that, we still have found nothing!
 .  if empty(PGSQL_VER)
Index: Mk/bsd.default-versions.mk
===================================================================
--- Mk/bsd.default-versions.mk
+++ Mk/bsd.default-versions.mk
@@ -72,7 +72,17 @@
 PERL5_DEFAULT:=		${_PERL5_FROM_BIN:R}
 .endif
 # Possible values: 9.2, 9.3, 9.4, 9.5, 9.6
+_PG_CONFIG=	${LOCALBASE}/bin/pg_config
+.if !exists(${_PG_CONFIG}) || (!defined(_PORTS_ENV_CHECK) && \
+    defined(PACKAGE_BUILDING))
 PGSQL_DEFAULT?=		9.5
+.elif !defined(PGSQL_DEFAULT)
+.if !defined(_PGSQL_FROM_CONFIG)
+_PGSQL_FROM_CONFIG!=	${_PG_CONFIG} --version | ${SED} -n 's/PostgreSQL[^0-9]*\([0-9]\.*[0-9]\).*/\1/p'
+.endif
+_EXPORTED_VARS+=	_PGSQL_FROM_CONFIG
+PGSQL_DEFAULT:=		${_PGSQL_FROM_CONFIG}
+.endif
 # Possible values: 5.6, 7.0, 7.1
 PHP_DEFAULT?=		5.6
 # Possible values: 2.7, 3.3, 3.4, 3.5, 3.6