diff --git a/pymatviz/histogram.py b/pymatviz/histogram.py
index 46788234..64333164 100644
--- a/pymatviz/histogram.py
+++ b/pymatviz/histogram.py
@@ -55,7 +55,7 @@ def elements_hist(
     Args:
         formulas (list[str]): compositional strings, e.g. ["Fe2O3", "Bi2Te3"].
         count_mode ("composition" | "fractional_composition" | "reduced_composition"):
-            Reduce or normalize compositions before counting. See count_elements() for
+            Reduce or normalize compositions before counting. See `count_elements` for
             details. Only used when formulas is list of composition strings/objects.
         log (bool, optional): Whether y-axis is log or linear. Defaults to False.
         keep_top (int | None): Display only the top n elements by prevalence.
diff --git a/pymatviz/ptable/ptable_matplotlib.py b/pymatviz/ptable/ptable_matplotlib.py
index 0a55c656..300d8e14 100644
--- a/pymatviz/ptable/ptable_matplotlib.py
+++ b/pymatviz/ptable/ptable_matplotlib.py
@@ -377,7 +377,7 @@ def ptable_heatmap_ratio(
 
         --- Data preprocessing ---
         count_mode ("composition" | "fractional_composition" | "reduced_composition"):
-            Reduce or normalize compositions before counting. See count_elements() for
+            Reduce or normalize compositions before counting. See `count_elements` for
             details. Only used when values is list of composition strings/objects.
         normalize (bool): Whether to normalize heatmap values so they sum to 1. Makes
             different ptable_heatmap_ratio plots comparable. Defaults to False.
@@ -418,8 +418,8 @@ def ptable_heatmap_ratio(
         plt.Figure: matplotlib Figure object.
     """
     # Generate ratio data
-    values_num = count_elements(values_num, count_mode)
-    values_denom = count_elements(values_denom, count_mode)
+    values_num = count_elements(values_num, count_mode, fill_value=0)
+    values_denom = count_elements(values_denom, count_mode, fill_value=0)
 
     values = values_num / values_denom