Index: head/Mk/Uses/python.mk
===================================================================
--- head/Mk/Uses/python.mk
+++ head/Mk/Uses/python.mk
@@ -383,7 +383,11 @@
 PYTHON_ABIVER=		# empty
 PYTHON_PORTSDIR=	${_PYTHON_RELPORTDIR}${PYTHON_SUFFIX}
 PYTHON_PORTVERSION!=	${MAKE} -V PORTVERSION -C ${PYTHON_PORTSDIR}
-PYTHON_REL=		${PYTHON_PORTVERSION:C/\.([0-9]+)$/.0\1/:C/\.0?([0-9][0-9])$/.\1/:S/.//g}
+# Create a 4 integer version string, prefixing 0 to the last token if
+# it's a single character. Only use the the first 3 tokens of
+# PORTVERSION to support pre-release versions (rc3, alpha4, etc) of
+# any Python port (lang/pythonXY)
+PYTHON_REL=	${PYTHON_PORTVERSION:C/^([0-9]+\.[0-9]+\.[0-9]+).*/\1/:C/\.([0-9]+)$/.0\1/:C/\.0?([0-9][0-9])$/.\1/:S/.//g}
 
 # Might be overridden by calling ports
 PYTHON_CMD?=		${_PYTHON_BASECMD}${_PYTHON_VERSION}