Index: Mk/Uses/python.mk
===================================================================
--- Mk/Uses/python.mk
+++ Mk/Uses/python.mk
@@ -246,6 +246,20 @@
 _PYTHON_BASECMD=		${LOCALBASE}/bin/python
 _PYTHON_RELPORTDIR=		lang/python
 
+# List all valid USE_PYTHON features here
+_VALID_PYTHON_FEATURES=	allflavors autoplist concurrent cython cython_run \
+			distutils flavors noegginfo noflavors optsuffix \
+			py3kplist pythonprefix
+_INVALID_PYTHON_FEATURES=
+.for var in ${USE_PYTHON}
+.  if empty(_VALID_PYTHON_FEATURES:M${var})
+_INVALID_PYTHON_FEATURES+=	${var}
+.  endif
+.endfor
+.if !empty(_INVALID_PYTHON_FEATURES)
+IGNORE+=	uses unknown USE_PYTHON features: ${_INVALID_PYTHON_FEATURES}
+.endif
+
 # Make each individual feature available as _PYTHON_FEATURE_<FEATURENAME>
 .for var in ${USE_PYTHON}
 _PYTHON_FEATURE_${var:C/=.*$//:tu}=	${var:C/.*=//:S/,/ /g}