--- lang/ghc/Makefile
+++ lang/ghc/Makefile
@@ -163,7 +163,7 @@
 
 # override TMPDIR because /tmp often doesn't have enough space
 # to build some of the larger libraries.
-TMPDIR=		${WRKSRC}/tmp
+TMPDIR?=	${WRKSRC}/tmp
 
 # Defining with documentation:
 # An in place installation and registration of hscolour will be