diff --git a/R/sample_filtering.R b/R/sample_filtering.R
index 9f3f76d..07363a4 100644
--- a/R/sample_filtering.R
+++ b/R/sample_filtering.R
@@ -56,10 +56,13 @@ simple_FNR_params = function(expr, pos_controls, fn_tresh = 0.01) {
   # Median log-expression in positive observations
   mu_obs = log(rowMedians(pos_expr, na.rm = TRUE))
   if (any(is.na(mu_obs))) {
+    na_rows <- (1:nrow(expr))[pos_controls][which(is.na(mu_obs))]
+    na_rowsm <- paste(na_rows, sep=", ")
     stop(
       paste0(
         "Median log-expression in positive ",
-        "observations NA for some positive control gene/s"
+        "observations NA for some positive control gene/s in rows: ",
+        na_rowsm
       )
     )
   }
@@ -869,4 +872,4 @@ factor_sample_filter = function(expr,
     warning("No z-cutoff specified, thus no filtering results returned.")
     return(NA)
   }
-}
\ No newline at end of file
+}