diff --git a/Mk/defaults.mk b/Mk/defaults.mk
index 1422232d2..b6fac0244 100644
--- a/Mk/defaults.mk
+++ b/Mk/defaults.mk
@@ -51,6 +51,13 @@ PLUGIN_FLAVOUR?=	Base
 .endif
 .endif
 
+VERSIONBIN=	${LOCALBASE}/sbin/opnsense-version
+
+.if exists(${VERSIONBIN})
+_PLUGIN_ABI!=	${VERSIONBIN} -a
+PLUGIN_ABI?=	${_PLUGIN_ABI}
+.endif
+
 PHPBIN=		${LOCALBASE}/bin/php
 
 .if exists(${PHPBIN})
@@ -65,9 +72,11 @@ _PLUGIN_PYTHON!=${PYTHONLINK} -V
 PLUGIN_PYTHON?=	${_PLUGIN_PYTHON:[2]:S/./ /g:[1..2]:tW:S/ //}
 .endif
 
-PLUGIN_ABI?=	21.1
-PLUGIN_PHP?=	74
-PLUGIN_PYTHON?=	37
+.for REPLACEMENT in ABI PHP PYTHON
+. if empty(PLUGIN_${REPLACEMENT})
+.  error Cannot build without PLUGIN_${REPLACEMENT} set
+. endif
+.endfor
 
 REPLACEMENTS=	PLUGIN_ABI \
 		PLUGIN_ARCH \