diff --git a/miscplot/variability.py b/miscplot/variability.py
index 51b7e3a..63cd99d 100644
--- a/miscplot/variability.py
+++ b/miscplot/variability.py
@@ -67,7 +67,7 @@ def variability_plot(
     # Assign category indicies (x_pos)
     df = df.sort(groups)
     df_groups = df.select(groups).unique(maintain_order=True).with_row_index(name='x_pos')
-    df = df.join(df_groups, on=groups, maintain_order='left')
+    df = df.join(df_groups, on=groups, maintain_order='left', nulls_equal=True)
     max_group_length = df.group_by(groups).len().select('len').max()[0, 0]   # How many points in the largest x_pos
 
     # Add jitter to the scatterplots-plots