diff --git a/Makefile.inc1 b/Makefile.inc1
index 5e8c0d584af6..249cd5be2dd0 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1152,7 +1152,7 @@ reinstallkernel reinstallkernel.debug: _installcheck_kernel .PHONY
 	    ${CROSSENV} PATH=${TMPPATH} \
 	    ${MAKE} ${IMAKE_INSTALL} KERNEL=${INSTKERNNAME} ${.TARGET:S/kernel//}
 .endif
-.if ${BUILDKERNELS:[#]} > 1 && !defined(NO_INSTALLEXTRAKERNELS)
+.if ${BUILDKERNELS:[#]} > 1 && ${NO_INSTALLEXTRAKERNELS} != "yes"
 .for _kernel in ${BUILDKERNELS:[2..-1]}
 	@echo "--------------------------------------------------------------"
 	@echo ">>> Installing kernel ${_kernel}"
@@ -1183,7 +1183,7 @@ distributekernel distributekernel.debug: .PHONY
 	    ${DESTDIR}/${DISTDIR}/kernel.meta
 .endif
 .endif
-.if ${BUILDKERNELS:[#]} > 1 && !defined(NO_INSTALLEXTRAKERNELS)
+.if ${BUILDKERNELS:[#]} > 1 && ${NO_INSTALLEXTRAKERNELS} != "yes"
 .for _kernel in ${BUILDKERNELS:[2..-1]}
 .if defined(NO_ROOT)
 	@echo "#${MTREE_MAGIC}" > ${DESTDIR}/${DISTDIR}/kernel.${_kernel}.premeta
@@ -1214,7 +1214,7 @@ packagekernel: .PHONY
 	    tar cvf - --include '*/*/*.debug' \
 	    @${DESTDIR}/${DISTDIR}/kernel.meta | \
 	    ${XZ_CMD} > ${DESTDIR}/${DISTDIR}/kernel-dbg.txz
-.if ${BUILDKERNELS:[#]} > 1 && !defined(NO_INSTALLEXTRAKERNELS)
+.if ${BUILDKERNELS:[#]} > 1 && ${NO_INSTALLEXTRAKERNELS} != "yes"
 .for _kernel in ${BUILDKERNELS:[2..-1]}
 	cd ${DESTDIR}/${DISTDIR}/kernel.${_kernel}; \
 	    tar cvf - --exclude '*.debug' \
@@ -1235,7 +1235,7 @@ packagekernel: .PHONY
 	cd ${DESTDIR}/${DISTDIR}/kernel; \
 	    tar cvf - --include '*/*/*.debug' $$(eval find .) | \
 	    ${XZ_CMD} > ${DESTDIR}/${DISTDIR}/kernel-dbg.txz
-.if ${BUILDKERNELS:[#]} > 1 && !defined(NO_INSTALLEXTRAKERNELS)
+.if ${BUILDKERNELS:[#]} > 1 && ${NO_INSTALLEXTRAKERNELS} != "yes"
 .for _kernel in ${BUILDKERNELS:[2..-1]}
 	cd ${DESTDIR}/${DISTDIR}/kernel.${_kernel}; \
 	    tar cvf - --exclude '*.debug' . | \
@@ -1345,7 +1345,7 @@ create-kernel-packages:	_pkgbootstrap .PHONY
 		-o ${REPODIR}/$$(pkg -o ABI_FILE=${WSTAGEDIR}/bin/sh config ABI)/${PKG_VERSION}
 .endfor
 .endif
-.if ${BUILDKERNELS:[#]} > 1 && !defined(NO_INSTALLEXTRAKERNELS)
+.if ${BUILDKERNELS:[#]} > 1 && ${NO_INSTALLEXTRAKERNELS} != "yes"
 .for _kernel in ${BUILDKERNELS:[2..-1]}
 .if exists(${KSTAGEDIR}/kernel.${_kernel}.meta)
 .for flavor in "" -debug