diff -rU4 Rcpp-orig/src/Module.cpp Rcpp-patched/src/Module.cpp
--- Rcpp-orig/src/Module.cpp	2013-03-23 14:53:30.000000000 +0000
+++ Rcpp-patched/src/Module.cpp	2013-06-13 09:22:06.486206400 +0100
@@ -27,9 +27,9 @@
 #define UNPACK_EXTERNAL_ARGS(__CARGS__,__P__)    \
 SEXP __CARGS__[MAX_ARGS] ;                       \
 int nargs = 0 ;                                  \
 for(; nargs<MAX_ARGS; nargs++){                  \
-	if( p == R_NilValue ) break ;                \
+	if( __P__ == R_NilValue ) break ;            \
 	__CARGS__[nargs] = CAR(__P__) ;              \
 	__P__ = CDR(__P__) ;                         \
 }