diff --git a/R/RcppExports.R b/R/RcppExports.R
index b42a4a4..2fd63db 100644
--- a/R/RcppExports.R
+++ b/R/RcppExports.R
@@ -1,89 +1,89 @@
-# Generated by using Rcpp::compileAttributes() -> do not edit by hand
-# Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
-
-#' Calculate IBD probabilities
-#'
-#' Calculate IBD probabilities for different types of populations.
-#'
-#' IBD probabilities can be calculated for many different types of populations.
-#' In the following table all supported populations are listed. Note that the
-#' value of x in the population types is variable, with its maximum value
-#' depicted in the last column.
-#'
-#' | __Population type__ | __Cross__ | __Description__ | __max. x__ |
-#' | ------ | ----------------- | -------------------------------------- | --- |
-#' | DH | biparental | doubled haploid population | |
-#' | Fx | biparental | Fx population (F1, followed by x-1 generations of selfing) | 8 |
-#' | FxDH | biparental | Fx, followed by DH generation | 8 |
-#' | BCx | biparental | backcross, second parent is recurrent parent | 9 |
-#' | BCxDH | biparental | BCx, followed by DH generation | 9 |
-#' | BC1Sx | biparental | BC1, followed by x generations of selfing | 7 |
-#' | BC1SxDH | biparental | BC1, followed by x generations of selfing and DH | 6 |
-#' | C3 | three-way | three way cross: (AxB) x C |  |
-#' | C3DH | three-way | C3, followed by DH generation |  |
-#' | C3Sx | three-way | C3, followed by x generations of selfing | 7 |
-#' | C3SxDH | three-way | C3, followed by x generations of selfing and DH generation | 6 |
-#' | C4 | four-way | four-way cross: (AxB) x (CxD)	| |
-#' | C4DH | four-way | C4, followed by DH generation |  |
-#' | C4Sx | four-way | C4, followed by x generations of selfing | 6 |
-#' | C4SxDH | four-way | C4, followed by x generations of selfing and DH generation | 6 |
-#'
-#' @param popType A character string indicating the type of population. One of
-#' DH, Fx, FxDH, BCx, BCxDH, BC1Sx, BC1SxDH, C3, C3DH, C3Sx, C3SxDH, C4, C4DH,
-#' C4Sx, C4SxDH (see Details).
-#' @param markerFile A character string indicating the location of the file with
-#' genotypic information for the population. The file should be in
-#' tab-delimited format with a header containing marker names.
-#' @param mapFile A character string indicating the location of the map file
-#' for the population. The file should be in tab-delimited format. It should
-#' consist of exactly three columns, marker, chromosome and position. There
-#' should be no header. The positions in the file should be in centimorgan.
-#' @param evalPos A data.frame with evaluation positions to which the
-#' calculations should be limited.
-#' @param evalDist An optional numerical value indicating the maximum
-#' distance for marker positions. Extra markers will be added based on the
-#' value of \code{grid}.
-#' @param grid Should the extra markers that are added to assure the a
-#' maximum distince of \code{evalDist} be on a grid (\code{TRUE}) or in between
-#' marker existing marker positions (\code{FALSE}).
-#' @param verbose Should messages indicating the progress of the process be
-#' printed?
-#'
-#' @returns An object of class \code{IBDprob}, a \code{list} with five elements,
-#' \describe{
-#' \item{map}{a \code{data.frame} with chromosome and position of the markers.}
-#' \item{markers}{a 3-dimensional \code{array} of IBD probabilities with
-#' genotypes, markers and parents as array dimensions.}
-#' \item{parents}{the parents.}
-#' \item{popType}{the population type.}
-#' }
-#'
-#' @examples
-#' ## Compute IBD probabilities for Steptoe Morex.
-#' SxMIBD <- calcIBD(popType = "DH",
-#'                   markerFile = system.file("extdata/SxM", "SxM_geno.txt",
-#'                                         package = "statgenIBD"),
-#'                   mapFile = system.file("extdata/SxM", "SxM_map.txt",
-#'                                         package = "statgenIBD"))
-#'
-#' ## Check summary.
-#' summary(SxMIBD)
-#'
-#' ## Compute IBD probabilities for Steptoe Morex.
-#' ## Add extra evaluation positions in between exiting marker positions
-#' ## to assure evaluation positions are at most 5 cM apart.
-#' SxMIBD_Ext <- calcIBD(popType = "DH",
-#'                       markerFile = system.file("extdata/SxM", "SxM_geno.txt",
-#'                                               package = "statgenIBD"),
-#'                       mapFile = system.file("extdata/SxM", "SxM_map.txt",
-#'                                             package = "statgenIBD"),
-#'                       evalDist = 5)
-#'
-#' ## Check summary.
-#' summary(SxMIBD_Ext)
-#'
-#' @export
-calcIBD <- function(popType, markerFile, mapFile, evalPos = NULL, evalDist = NULL, grid = TRUE, verbose = FALSE) {
-    .Call(`_statgenIBD_calcIBD`, popType, markerFile, mapFile, evalPos, evalDist, grid, verbose)
-}
-
+# Generated by using Rcpp::compileAttributes() -> do not edit by hand
+# Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
+
+#' Calculate IBD probabilities
+#'
+#' Calculate IBD probabilities for different types of populations.
+#'
+#' IBD probabilities can be calculated for many different types of populations.
+#' In the following table all supported populations are listed. Note that the
+#' value of x in the population types is variable, with its maximum value
+#' depicted in the last column.
+#'
+#' | __Population type__ | __Cross__ | __Description__ | __max. x__ |
+#' | ------ | ----------------- | -------------------------------------- | --- |
+#' | DH | biparental | doubled haploid population | |
+#' | Fx | biparental | Fx population (F1, followed by x-1 generations of selfing) | 8 |
+#' | FxDH | biparental | Fx, followed by DH generation | 8 |
+#' | BCx | biparental | backcross, second parent is recurrent parent | 9 |
+#' | BCxDH | biparental | BCx, followed by DH generation | 9 |
+#' | BC1Sx | biparental | BC1, followed by x generations of selfing | 7 |
+#' | BC1SxDH | biparental | BC1, followed by x generations of selfing and DH | 6 |
+#' | C3 | three-way | three way cross: (AxB) x C |  |
+#' | C3DH | three-way | C3, followed by DH generation |  |
+#' | C3Sx | three-way | C3, followed by x generations of selfing | 7 |
+#' | C3SxDH | three-way | C3, followed by x generations of selfing and DH generation | 6 |
+#' | C4 | four-way | four-way cross: (AxB) x (CxD)	| |
+#' | C4DH | four-way | C4, followed by DH generation |  |
+#' | C4Sx | four-way | C4, followed by x generations of selfing | 6 |
+#' | C4SxDH | four-way | C4, followed by x generations of selfing and DH generation | 6 |
+#'
+#' @param popType A character string indicating the type of population. One of
+#' DH, Fx, FxDH, BCx, BCxDH, BC1Sx, BC1SxDH, C3, C3DH, C3Sx, C3SxDH, C4, C4DH,
+#' C4Sx, C4SxDH (see Details).
+#' @param markerFile A character string indicating the location of the file with
+#' genotypic information for the population. The file should be in
+#' tab-delimited format with a header containing marker names.
+#' @param mapFile A character string indicating the location of the map file
+#' for the population. The file should be in tab-delimited format. It should
+#' consist of exactly three columns, marker, chromosome and position. There
+#' should be no header. The positions in the file should be in centimorgan.
+#' @param evalPos A data.frame with evaluation positions to which the
+#' calculations should be limited.
+#' @param evalDist An optional numerical value indicating the maximum
+#' distance for marker positions. Extra markers will be added based on the
+#' value of \code{grid}.
+#' @param grid Should the extra markers that are added to assure the a
+#' maximum distince of \code{evalDist} be on a grid (\code{TRUE}) or in between
+#' marker existing marker positions (\code{FALSE}).
+#' @param verbose Should messages indicating the progress of the process be
+#' printed?
+#'
+#' @returns An object of class \code{IBDprob}, a \code{list} with five elements,
+#' \describe{
+#' \item{map}{a \code{data.frame} with chromosome and position of the markers.}
+#' \item{markers}{a 3-dimensional \code{array} of IBD probabilities with
+#' genotypes, markers and parents as array dimensions.}
+#' \item{parents}{the parents.}
+#' \item{popType}{the population type.}
+#' }
+#'
+#' @examples
+#' ## Compute IBD probabilities for Steptoe Morex.
+#' SxMIBD <- calcIBD(popType = "DH",
+#'                   markerFile = system.file("extdata/SxM", "SxM_geno.txt",
+#'                                         package = "statgenIBD"),
+#'                   mapFile = system.file("extdata/SxM", "SxM_map.txt",
+#'                                         package = "statgenIBD"))
+#'
+#' ## Check summary.
+#' summary(SxMIBD)
+#'
+#' ## Compute IBD probabilities for Steptoe Morex.
+#' ## Add extra evaluation positions in between exiting marker positions
+#' ## to assure evaluation positions are at most 5 cM apart.
+#' SxMIBD_Ext <- calcIBD(popType = "DH",
+#'                       markerFile = system.file("extdata/SxM", "SxM_geno.txt",
+#'                                               package = "statgenIBD"),
+#'                       mapFile = system.file("extdata/SxM", "SxM_map.txt",
+#'                                             package = "statgenIBD"),
+#'                       evalDist = 5)
+#'
+#' ## Check summary.
+#' summary(SxMIBD_Ext)
+#'
+#' @export
+calcIBD <- function(popType, markerFile, mapFile, evalPos = NULL, evalDist = NULL, grid = TRUE, verbose = FALSE) {
+    .Call(`_statgenIBD_calcIBD`, popType, markerFile, mapFile, evalPos, evalDist, grid, verbose)
+}
+
diff --git a/src/RcppExports.cpp b/src/RcppExports.cpp
index 593714d..9c08bc0 100644
--- a/src/RcppExports.cpp
+++ b/src/RcppExports.cpp
@@ -1,40 +1,40 @@
-// Generated by using Rcpp::compileAttributes() -> do not edit by hand
-// Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
-
-#include <RcppArmadillo.h>
-#include <Rcpp.h>
-
-using namespace Rcpp;
-
-#ifdef RCPP_USE_GLOBAL_ROSTREAM
-Rcpp::Rostream<true>&  Rcpp::Rcout = Rcpp::Rcpp_cout_get();
-Rcpp::Rostream<false>& Rcpp::Rcerr = Rcpp::Rcpp_cerr_get();
-#endif
-
-// calcIBD
-List calcIBD(CharacterVector& popType, CharacterVector& markerFile, CharacterVector& mapFile, Nullable<DataFrame&> evalPos, Nullable<NumericVector&> evalDist, const bool& grid, const bool& verbose);
-RcppExport SEXP _statgenIBD_calcIBD(SEXP popTypeSEXP, SEXP markerFileSEXP, SEXP mapFileSEXP, SEXP evalPosSEXP, SEXP evalDistSEXP, SEXP gridSEXP, SEXP verboseSEXP) {
-BEGIN_RCPP
-    Rcpp::RObject rcpp_result_gen;
-    Rcpp::RNGScope rcpp_rngScope_gen;
-    Rcpp::traits::input_parameter< CharacterVector& >::type popType(popTypeSEXP);
-    Rcpp::traits::input_parameter< CharacterVector& >::type markerFile(markerFileSEXP);
-    Rcpp::traits::input_parameter< CharacterVector& >::type mapFile(mapFileSEXP);
-    Rcpp::traits::input_parameter< Nullable<DataFrame&> >::type evalPos(evalPosSEXP);
-    Rcpp::traits::input_parameter< Nullable<NumericVector&> >::type evalDist(evalDistSEXP);
-    Rcpp::traits::input_parameter< const bool& >::type grid(gridSEXP);
-    Rcpp::traits::input_parameter< const bool& >::type verbose(verboseSEXP);
-    rcpp_result_gen = Rcpp::wrap(calcIBD(popType, markerFile, mapFile, evalPos, evalDist, grid, verbose));
-    return rcpp_result_gen;
-END_RCPP
-}
-
-static const R_CallMethodDef CallEntries[] = {
-    {"_statgenIBD_calcIBD", (DL_FUNC) &_statgenIBD_calcIBD, 7},
-    {NULL, NULL, 0}
-};
-
-RcppExport void R_init_statgenIBD(DllInfo *dll) {
-    R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
-    R_useDynamicSymbols(dll, FALSE);
-}
+// Generated by using Rcpp::compileAttributes() -> do not edit by hand
+// Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
+
+#include <RcppArmadillo.h>
+#include <Rcpp.h>
+
+using namespace Rcpp;
+
+#ifdef RCPP_USE_GLOBAL_ROSTREAM
+Rcpp::Rostream<true>&  Rcpp::Rcout = Rcpp::Rcpp_cout_get();
+Rcpp::Rostream<false>& Rcpp::Rcerr = Rcpp::Rcpp_cerr_get();
+#endif
+
+// calcIBD
+List calcIBD(CharacterVector& popType, CharacterVector& markerFile, CharacterVector& mapFile, Nullable<DataFrame> evalPos, Nullable<NumericVector> evalDist, const bool& grid, const bool& verbose);
+RcppExport SEXP _statgenIBD_calcIBD(SEXP popTypeSEXP, SEXP markerFileSEXP, SEXP mapFileSEXP, SEXP evalPosSEXP, SEXP evalDistSEXP, SEXP gridSEXP, SEXP verboseSEXP) {
+BEGIN_RCPP
+    Rcpp::RObject rcpp_result_gen;
+    Rcpp::RNGScope rcpp_rngScope_gen;
+    Rcpp::traits::input_parameter< CharacterVector& >::type popType(popTypeSEXP);
+    Rcpp::traits::input_parameter< CharacterVector& >::type markerFile(markerFileSEXP);
+    Rcpp::traits::input_parameter< CharacterVector& >::type mapFile(mapFileSEXP);
+    Rcpp::traits::input_parameter< Nullable<DataFrame> >::type evalPos(evalPosSEXP);
+    Rcpp::traits::input_parameter< Nullable<NumericVector> >::type evalDist(evalDistSEXP);
+    Rcpp::traits::input_parameter< const bool& >::type grid(gridSEXP);
+    Rcpp::traits::input_parameter< const bool& >::type verbose(verboseSEXP);
+    rcpp_result_gen = Rcpp::wrap(calcIBD(popType, markerFile, mapFile, evalPos, evalDist, grid, verbose));
+    return rcpp_result_gen;
+END_RCPP
+}
+
+static const R_CallMethodDef CallEntries[] = {
+    {"_statgenIBD_calcIBD", (DL_FUNC) &_statgenIBD_calcIBD, 7},
+    {NULL, NULL, 0}
+};
+
+RcppExport void R_init_statgenIBD(DllInfo *dll) {
+    R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
+    R_useDynamicSymbols(dll, FALSE);
+}
diff --git a/src/calcIBD.cpp b/src/calcIBD.cpp
index e0e4317..de59791 100644
--- a/src/calcIBD.cpp
+++ b/src/calcIBD.cpp
@@ -99,8 +99,8 @@ using namespace ibd;
 List calcIBD(CharacterVector& popType,
              CharacterVector& markerFile,
              CharacterVector& mapFile,
-             Nullable<DataFrame&> evalPos = R_NilValue,
-             Nullable<NumericVector&> evalDist = R_NilValue,
+             Nullable<DataFrame> evalPos = R_NilValue,
+             Nullable<NumericVector> evalDist = R_NilValue,
              const bool& grid = true,
              const bool& verbose = false)
 {
@@ -126,7 +126,7 @@ List calcIBD(CharacterVector& popType,
                    _poptype,
                    Rcpp::as<std::string>(markerFile),
                    Rcpp::as<std::string>(mapFile),
-                   evalPos,
+                   Rcpp::DataFrame(evalPos),
                    max_step_size,
                    grid,
                    verbose);