diff --git a/HISTORY.rst b/HISTORY.rst
index 2ace1a9..8063f30 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,6 +1,10 @@
 =======
 History
 =======
+2024.6.5 -- Bugfix: Handling of duplicates in lists
+    * Roundoff in floating point numbers caused some duplicates to be missed. The code
+      now checks for duplicates in a more robust way.
+      
 2024.4.30 -- Added utility for handling list definitions
     * Add list_definition.py with parse_list()
     * Updated makefile for doctests.
diff --git a/seamm_util/list_definition.py b/seamm_util/list_definition.py
index 1f837d8..a916f52 100644
--- a/seamm_util/list_definition.py
+++ b/seamm_util/list_definition.py
@@ -131,8 +131,12 @@ def parse_list(input, duplicates=True, sort=False, **kwargs):
 
             # Add a very small number for roundoff in floats
             while sign * (stop - value + stop / 1.0e8) >= 0:
-                if not duplicates and value in result:
-                    pass
+                if not duplicates:
+                    for tmp in result:
+                        if abs(value - tmp) < 1.0e-8:
+                            break
+                    else:
+                        result.append(value)
                 else:
                     result.append(value)
                 value += step