diff --git a/R/pid.R b/R/pid.R
index 8b67028..71d1a2f 100644
--- a/R/pid.R
+++ b/R/pid.R
@@ -65,5 +65,10 @@ specific_information <- function(probabilities, source="x1", target="z") {
   term1 <- sweep(apply(probabilities, c(source, target), sum), 2, apply(probabilities, target, sum), "/")
   term2 <- log2(apply(probabilities, c(source,target), sum) / outer_prod)
 
-  colSums(apply(term1 * term2, 2, function(x) {x[is.nan(x)] <- 0; x}))
+  prod <- apply(term1 * term2, 2, function(x) {x[is.nan(x)] <- 0; x})
+  if(is.null(dim(prod))) {
+    return(prod)
+  } else {
+    return(colSums(prod))
+  }
 }