diff --git a/CHANGES b/CHANGES
index dee0e09f..613ff8c5 100644
--- a/CHANGES
+++ b/CHANGES
@@ -30,6 +30,8 @@ Enhancements
 
 Fixes
 
+* for mdpow.workflows.dihedrals.periodic_angle() implement .copy(deep=True)
+  to explicitly make a copy DataFrame of the data for angle padding (#242)
 * fix rcoulomb in CHARMM energy minimization MDP template file (PR #210)
 * fix ensemble.EnsembleAnalysis.check_groups_from_common_ensemble (#212)
 
diff --git a/mdpow/workflows/dihedrals.py b/mdpow/workflows/dihedrals.py
index a9ae5036..63b4d6a1 100644
--- a/mdpow/workflows/dihedrals.py
+++ b/mdpow/workflows/dihedrals.py
@@ -418,11 +418,11 @@ def periodic_angle(df, padding=45):
 
     '''
 
-    df1 = df[df.dihedral > 180 - padding]
+    df1 = df[df.dihedral > 180 - padding].copy(deep=True)
     df1.dihedral -= 360
-    df2 = df[df.dihedral < -180 + padding]
+    df2 = df[df.dihedral < -180 + padding].copy(deep=True)
     df2.dihedral += 360
-    df_aug = pd.concat([df1, df, df2]).reset_index()
+    df_aug = pd.concat([df1, df, df2]).reset_index(drop=True)
 
     return df_aug