diff --git a/Makefile.inc1 b/Makefile.inc1
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1356,28 +1356,6 @@
 .endif
 .endif
 
-#
-# Don't allow installworld or installkernel on a pkgbase system.  This avoids
-# accidentally updating a pkgbase system with install{world,kernel}, causing
-# the installed system to become out of date with the package database.
-#
-# Skip the check if DESTDIR is defined on the assumption the user knows what
-# they're doing.  This means the check can be disabled for the running system
-# using DESTDIR=/.
-#
-.if !make(distributeworld) && !defined(DESTDIR)
-_installcheck_world: __installcheck_PKG
-_installcheck_kernel: __installcheck_PKG
-__installcheck_PKG: .PHONY
-.if exists(${LOCALBASE}/sbin/pkg-static)
-	@if ${LOCALBASE}/sbin/pkg-static info -e ${PKG_NAME_PREFIX}-runtime; then \
-		echo >&2 "ERROR: This target should not be used on a system installed from packages." ; \
-		echo >&2 "       To override this check, set DESTDIR=/."; \
-		false; \
-	fi
-.endif
-.endif
-
 .if !defined(DB_FROM_SRC)
 #
 # Check for missing UIDs/GIDs.
@@ -1873,6 +1851,67 @@
 .endif
 .endif
 
+#
+# Don't allow installworld or installkernel on a pkgbase system.  This avoids
+# accidentally updating a pkgbase system with install{world,kernel}, causing
+# the installed system to become out of date with the package database.
+#
+# Skip the check if DESTDIR is defined on the assumption the user knows what
+# they're doing.  This means the check can be disabled for the running system
+# using DESTDIR=/.
+#
+# People who want to disable this check permanently may set two variables in
+# /etc/make.conf, ALLOW_PKGBASE_INSTALLKERNEL and ALLOW_PKGBASE_INSTALLWORLD,
+# to disable these checks.  That doesn't stop this from breaking your system,
+# it just stops make from warning about it.
+#
+.if !make(distributeworld) && !defined(DESTDIR)
+
+. if !defined(ALLOW_PKGBASE_INSTALLKERNEL) && exists(${LOCALBASE}/sbin/pkg-static)
+# For installkernel, we check if this specific kernel was installed by pkg.
+# This means people can continue to use installkernel for non-packaged
+# kernels, which is useful for development.
+
+_installcheck_kernel: __installcheck_kernel_pkgbase
+__installcheck_kernel_pkgbase: .PHONY
+.  for _kernel in ${NO_INSTALLKERNEL:D:U${INSTKERNNAME}} \
+		${INSTALLEXTRAKERNELS:S/^/${INSTKERNNAME}./}
+	@if ${LOCALBASE}/sbin/pkg-static which /boot/${_kernel}/kernel \
+	    >/dev/null 2>&1; then \
+		echo >&2 "ERROR: The kernel at /boot/${_kernel} was installed from packages." ; \
+		echo >&2 "       A packaged kernel should never be updated using installkernel;" ; \
+		echo >&2 "       this will cause the package database to become out of sync with" ; \
+		echo >&2 "       the live system state.  Either uninstall the packaged kernel," ; \
+		echo >&2 "       or install this kernel to a different path using INSTKERNNAME." ; \
+		echo >&2 "" ; \
+		echo >&2 "       If you understand the risks and wish to proceed anyway, you may" ; \
+		echo >&2 "       set ALLOW_PKGBASE_INSTALLKERNEL=yes to override this safety check." ; \
+		echo >&2 "       After doing so, you should not use the pkg(8) utility until you" ; \
+		echo >&2 "       have resolved the inconsistency between the installed system and" ; \
+		echo >&2 "       the package database." ; \
+		false; \
+	fi
+.  endfor
+. endif	# !defined(ALLOW_PKGBASE_INSTALLKERNEL) && exists(pkg-static)
+
+. if !defined(ALLOW_PKGBASE_INSTALLWORLD) && exists(${LOCALBASE}/sbin/pkg-static)
+_installcheck_world: __installcheck_world_pkgbase
+__installcheck_world_pkgbase: .PHONY
+	@if ${LOCALBASE}/sbin/pkg-static info -e ${PKG_NAME_PREFIX}-runtime; then \
+		echo >&2 "ERROR: This target should never be used on a system installed from packages;" ; \
+		echo >&2 "       doing so will cause the package database to become out of sync with" ; \
+		echo >&2 "       the live system state." ; \
+		echo >&2 "" ; \
+		echo >&2 "       If you understand the risks and wish to proceed anyway, you may" ; \
+		echo >&2 "       set ALLOW_PKGBASE_INSTALLWORLD=yes to override this safety check." ; \
+		echo >&2 "       After doing so, you should not use the pkg(8) utility until you" ; \
+		echo >&2 "       have resolved the inconsistency between the installed system and" ; \
+		echo >&2 "       the package database." ; \
+		false; \
+	fi
+. endif	# !defined(ALLOW_PKGBASE_INSTALLWORLD) && exists(pkg-static)
+.endif	# !make(distributeworld) && !defined(DESTDIR)
+
 #
 # installkernel, etc.
 #