diff --git a/DESCRIPTION b/DESCRIPTION
index 904a59c8..74feca8e 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Type: Package
 Package: effectsize
 Title: Indices of Effect Size
-Version: 0.8.6.3
+Version: 0.8.6.4
 Authors@R: 
     c(person(given = "Mattan S.",
              family = "Ben-Shachar",
diff --git a/R/utils_validate_input_data.R b/R/utils_validate_input_data.R
index 3002ece0..0aa5e2f1 100644
--- a/R/utils_validate_input_data.R
+++ b/R/utils_validate_input_data.R
@@ -126,7 +126,7 @@
         return(mf)
       }
 
-      if (verbose && any(tapply(mf[[1]], mf[3:2], length) > 1L)) {
+      if (verbose && any(tapply(mf[[1]], mf[3:2], length) > 1L, na.rm = TRUE)) {
         insight::format_alert(
           paste0("The ", method, " standardized difference requires paired data,"),
           "but data contains more than one observation per design cell.",
diff --git a/tests/testthat/test-rm_d.R b/tests/testthat/test-rm_d.R
index af94290d..ed0c09e2 100644
--- a/tests/testthat/test-rm_d.R
+++ b/tests/testthat/test-rm_d.R
@@ -27,6 +27,12 @@ test_that("rm_d | paired data", {
     regexp = "replications"
   )
 
+  sleep[1, "extra"] <- NA
+  sleep2[1, "extra.1"] <- NA
+  expect_no_error(d1NA <- rm_d(extra ~ group | ID, data = sleep))
+  expect_no_error(d2NA <- rm_d(Pair(extra.1, extra.2) ~ 1, data = sleep2))
+  expect_equal(d1NA, d2NA)
+
 
   # equal with equal variance:
   dat <- data.frame(