Index: Mk/Uses/cmake.mk
===================================================================
--- Mk/Uses/cmake.mk
+++ Mk/Uses/cmake.mk
@@ -25,6 +25,8 @@
 #			Default: not set, unless BATCH or PACKAGE_BUILDING is defined
 #
 # Variables for ports:
+# CMAKE_ON		Appends -D<var>:bool=ON  to the CMAKE_ARGS,
+# CMAKE_OFF		Appends -D<var>:bool=OFF to the CMAKE_ARGS.
 # CMAKE_ARGS		- Arguments passed to cmake
 #			Default: see below
 # CMAKE_BUILD_TYPE	- Type of build (cmake predefined build types).
@@ -88,6 +90,13 @@
 			-DTHREADS_HAVE_PTHREAD_ARG:BOOL=YES \
 			-DCMAKE_INSTALL_RPATH_USE_LINK_PATH=YES \
 			-DCMAKE_VERBOSE_MAKEFILE:BOOL=ON
+
+# Handle the option-like CMAKE_ON and CMAKE_OFF lists.
+.for _bool_kind in ON OFF
+.  if defined(CMAKE_${_bool_kind})
+CMAKE_ARGS+=		${CMAKE_${_bool_kind}:C/.*/-D&:BOOL=${_bool_kind}/}
+.  endif
+.endfor
 
 CMAKE_INSTALL_PREFIX?=	${PREFIX}
 
Index: devel/cmake-doc/Makefile
===================================================================
--- devel/cmake-doc/Makefile
+++ devel/cmake-doc/Makefile
@@ -20,10 +20,9 @@
 USES=		cmake:outsource
 USE_QT5=	help_build
 
-CMAKE_ARGS=	-DSPHINX_MAN:BOOL=OFF \
-		-DSPHINX_HTML:BOOL=ON \
-		-DSPHINX_QTHELP:BOOL=ON \
-		-DCMAKE_DOC_DIR:STRING="${DOCSDIR_REL}" \
+CMAKE_OFF=	SPHINX_MAN
+CMAKE_ON=	SPHINX_HTML SPHINX_QTHELP
+CMAKE_ARGS=	-DCMAKE_DOC_DIR:STRING="${DOCSDIR_REL}" \
 		-DQCOLLECTIONGENERATOR_EXECUTABLE=${QT_BINDIR}/qcollectiongenerator
 CMAKE_SOURCE_PATH=	${WRKSRC}/Utilities/Sphinx
 
Index: devel/cmake-gui/Makefile
===================================================================
--- devel/cmake-gui/Makefile
+++ devel/cmake-gui/Makefile
@@ -22,13 +22,13 @@
 USE_QT5=	core gui widgets buildtools_build qmake_build
 USES=		cmake:run desktop-file-utils libarchive \
 		shared-mime-info
-CMAKE_ARGS=	-DBUILD_QtDialog:bool=on \
-		-DBUILD_CursesDialog:BOOL=OFF \
-		-DSPHINX_MAN:BOOL=ON \
-		-DCMAKE_USE_SYSTEM_LIBRARIES:BOOL=ON \
-		-DCMAKE_DATA_DIR:STRING="/${DATADIR_REL}" \
+CMAKE_OFF=	BUILD_CursesDialog \
+		CMake_SPHINX_DEPEND_ON_EXECUTABLES
+CMAKE_ON=	BUILD_QtDialog \
+		CMAKE_USE_SYSTEM_LIBRARIES \
+		SPHINX_MAN 
+CMAKE_ARGS=	-DCMAKE_DATA_DIR:STRING="/${DATADIR_REL}" \
 		-DCMAKE_DOC_DIR:STRING="/${DOCSDIR_REL}" \
-		-DCMake_SPHINX_DEPEND_ON_EXECUTABLES:BOOL=OFF
 
 ALL_TARGET=	cmake-gui documentation
 INSTALL_WRKSRC=	${WRKSRC}/Source/QtDialog