diff --git a/src/pycirclize/circos.py b/src/pycirclize/circos.py
index b705c7b..470515b 100644
--- a/src/pycirclize/circos.py
+++ b/src/pycirclize/circos.py
@@ -444,10 +444,10 @@ def initialize_from_matrix(
                 outer_track.xticks_by_interval(ticks_interval, **ticks_kws)
 
         # Plot links
-        fromto_label2color = {f"{t[0]}{t[1]}": t[2] for t in link_cmap}
+        fromto_label2color = {f"{t[0]}--->{t[1]}": t[2] for t in link_cmap}
         for link in matrix.to_links():
             from_label, to_label = link[0][0], link[1][0]
-            fromto_label = f"{from_label}{to_label}"
+            fromto_label = f"{from_label}--->{to_label}"
             # Set link color
             if fromto_label in fromto_label2color:
                 color = fromto_label2color[fromto_label]
diff --git a/src/pycirclize/parser/matrix.py b/src/pycirclize/parser/matrix.py
index 9692225..18af35d 100644
--- a/src/pycirclize/parser/matrix.py
+++ b/src/pycirclize/parser/matrix.py
@@ -103,7 +103,7 @@ def parse_fromto_table(
         for row in fromto_table.itertuples():
             from_label, to_label, value = str(row[1]), str(row[2]), row[3]
             if float(value) > 0:
-                fromto = f"{from_label}{to_label}"
+                fromto = f"{from_label}-->{to_label}"
                 fromto2value[fromto] = value
                 label2value_sum[from_label] += value
                 label2value_sum[to_label] += value
@@ -134,7 +134,7 @@ def parse_fromto_table(
         for row_label in all_labels:
             row_data = []
             for col_label in all_labels:
-                row_data.append(fromto2value[f"{row_label}{col_label}"])
+                row_data.append(fromto2value[f"{row_label}-->{col_label}"])
             matrix_data.append(row_data)
         matrix_df = pd.DataFrame(matrix_data, index=all_labels, columns=all_labels)