diff --git a/Mk/Uses/firebird.mk b/Mk/Uses/firebird.mk
index c5f72cd679c9..80c06442a251 100644
--- a/Mk/Uses/firebird.mk
+++ b/Mk/Uses/firebird.mk
@@ -1,22 +1,33 @@
 # Provide support for Firebird
 # Feature:	firebird
 # Usage:	USES=	firebird[:version]
 # MAINTAINER:	ports@FreeBSD.org
 
 .if !defined(_INCLUDE_USES_FIREBIRD_MK)
 _INCLUDE_USES_FIREBIRD_MK=	yes
 
 .if !empty(firebird_ARGS)
 FIREBIRD_VER=	${firebird_ARGS}
+.else
+FIREBIRD_VER=	${FIREBIRD_DEFAULT}
 .endif
 
-FIREBIRD_VER?=	${FIREBIRD_DEFAULT:S/.//}
-
 # When adding a version, please keep the comment in
 # Mk/bsd.default-versions.mk in sync.
-.if ${FIREBIRD_VER} == 25
-LIB_DEPENDS+=	libfbclient.so:databases/firebird25-client
-.else
-IGNORE=		cannot install: unknown Firebird version: ${FIREBIRD_VER}
-.endif
+VALID_FIREBIRD_VER=        2.5 3.0 4.0
+
+.for v in ${FIREBIRD_DEFAULT}
+.  if ! ${VALID_FIREBIRD_VER:M$v}
+IGNORE=		Invalid Firebird default version ${FIREBIRD_DEFAULT}; valid versions are ${VALID_FIREBIRD_VER}
+.  endif
+.endfor
+
+.for w in ${FIREBIRD_VER}
+.  if ! ${VALID_FIREBIRD_VER:M$w}
+IGNORE=		Invalid Firebird version ${FIREBIRD_VER}; valid versions are ${VALID_FIREBIRD_VER}
+.  endif
+.endfor
+
+LIB_DEPENDS+=	libfbclient.so:databases/firebird${FIREBIRD_VER:S/.//}-client
+
 .endif