diff --git a/src/System.Management.Automation/FormatAndOutput/common/DisplayDatabase/typeDataQuery.cs b/src/System.Management.Automation/FormatAndOutput/common/DisplayDatabase/typeDataQuery.cs
index 470832670a9..9e063988b08 100644
--- a/src/System.Management.Automation/FormatAndOutput/common/DisplayDatabase/typeDataQuery.cs
+++ b/src/System.Management.Automation/FormatAndOutput/common/DisplayDatabase/typeDataQuery.cs
@@ -588,7 +588,7 @@ private static bool IsOutOfBandView(ViewDefinition vd)
         /// <returns></returns>
         internal static AppliesTo GetAllApplicableTypes(TypeInfoDataBase db, AppliesTo appliesTo)
         {
-            Hashtable allTypes = new Hashtable(StringComparer.OrdinalIgnoreCase);
+            var allTypes = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
 
             foreach (TypeOrGroupReference r in appliesTo.referenceList)
             {
@@ -596,8 +596,8 @@ internal static AppliesTo GetAllApplicableTypes(TypeInfoDataBase db, AppliesTo a
                 TypeReference tr = r as TypeReference;
                 if (tr != null)
                 {
-                    if (!allTypes.ContainsKey(tr.name))
-                        allTypes.Add(tr.name, null);
+                    if (!allTypes.Contains(tr.name))
+                        allTypes.Add(tr.name);
                 }
                 else
                 {
@@ -616,16 +616,16 @@ internal static AppliesTo GetAllApplicableTypes(TypeInfoDataBase db, AppliesTo a
                     // we found the group, go over it
                     foreach (TypeReference x in tgd.typeReferenceList)
                     {
-                        if (!allTypes.ContainsKey(x.name))
-                            allTypes.Add(x.name, null);
+                        if (!allTypes.Contains(x.name))
+                            allTypes.Add(x.name);
                     }
                 }
             }
 
             AppliesTo retVal = new AppliesTo();
-            foreach (DictionaryEntry x in allTypes)
+            foreach (string x in allTypes)
             {
-                retVal.AddAppliesToType(x.Key as string);
+                retVal.AddAppliesToType(x);
             }
 
             return retVal;
diff --git a/src/System.Management.Automation/FormatAndOutput/common/Utilities/Mshexpression.cs b/src/System.Management.Automation/FormatAndOutput/common/Utilities/Mshexpression.cs
index bf3acfab2a1..e1af400ad51 100644
--- a/src/System.Management.Automation/FormatAndOutput/common/Utilities/Mshexpression.cs
+++ b/src/System.Management.Automation/FormatAndOutput/common/Utilities/Mshexpression.cs
@@ -231,19 +231,19 @@ public List<PSPropertyExpression> ResolveNames(PSObject target, bool expand)
                 }
             }
 
-            Hashtable hash = new Hashtable();
+            var allMembers = new HashSet<string>();
 
             // build the list of unique values: remove the possible duplicates
             // from property set expansion
             foreach (PSMemberInfo m in temporaryMemberList)
             {
-                if (!hash.ContainsKey(m.Name))
+                if (!allMembers.Contains(m.Name))
                 {
                     PSPropertyExpression ex = new PSPropertyExpression(m.Name);
 
                     ex._isResolved = true;
                     retVal.Add(ex);
-                    hash.Add(m.Name, null);
+                    allMembers.Add(m.Name);
                 }
             }
 
diff --git a/src/System.Management.Automation/help/AliasHelpProvider.cs b/src/System.Management.Automation/help/AliasHelpProvider.cs
index db7e4056d1e..670c0202bc7 100644
--- a/src/System.Management.Automation/help/AliasHelpProvider.cs
+++ b/src/System.Management.Automation/help/AliasHelpProvider.cs
@@ -141,7 +141,7 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
             {
                 string target = helpRequest.Target;
                 string pattern = target;
-                Hashtable hashtable = new Hashtable(StringComparer.OrdinalIgnoreCase);
+                var allAliases = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
 
                 if (!WildcardPattern.ContainsWildcardCharacters(target))
                 {
@@ -169,12 +169,12 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
                                 continue;
                             }
 
-                            if (hashtable.ContainsKey(name))
+                            if (allAliases.Contains(name))
                             {
                                 continue;
                             }
 
-                            hashtable.Add(name, null);
+                            allAliases.Add(name);
 
                             yield return helpInfo;
                         }
@@ -216,12 +216,12 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
                                 continue;
                             }
 
-                            if (hashtable.ContainsKey(name))
+                            if (allAliases.Contains(name))
                             {
                                 continue;
                             }
 
-                            hashtable.Add(name, null);
+                            allAliases.Add(name);
 
                             yield return helpInfo;
                         }
@@ -243,12 +243,12 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
 
                         HelpInfo helpInfo = AliasHelpInfo.GetHelpInfo(alias);
 
-                        if (hashtable.ContainsKey(name))
+                        if (allAliases.Contains(name))
                         {
                             continue;
                         }
 
-                        hashtable.Add(name, null);
+                        allAliases.Add(name);
 
                         yield return helpInfo;
                     }
diff --git a/src/System.Management.Automation/help/CommandHelpProvider.cs b/src/System.Management.Automation/help/CommandHelpProvider.cs
index 52e6b3e2916..aa3c1edb70e 100644
--- a/src/System.Management.Automation/help/CommandHelpProvider.cs
+++ b/src/System.Management.Automation/help/CommandHelpProvider.cs
@@ -427,7 +427,7 @@ internal override IEnumerable<HelpInfo> ExactMatchHelp(HelpRequest helpRequest)
             int countHelpInfosFound = 0;
             string target = helpRequest.Target;
             // this is for avoiding duplicate result from help output.
-            Hashtable hashtable = new Hashtable(StringComparer.OrdinalIgnoreCase);
+            var allHelpNames = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
 
             CommandSearcher searcher = GetCommandSearcherForExactMatch(target, _context);
 
@@ -453,7 +453,7 @@ internal override IEnumerable<HelpInfo> ExactMatchHelp(HelpRequest helpRequest)
                         throw new PSInvalidOperationException(HelpErrors.CircularDependencyInHelpForwarding);
                     }
 
-                    if (hashtable.ContainsKey(helpName))
+                    if (allHelpNames.Contains(helpName))
                         continue;
 
                     if (!Match(helpInfo, helpRequest, current))
@@ -462,7 +462,7 @@ internal override IEnumerable<HelpInfo> ExactMatchHelp(HelpRequest helpRequest)
                     }
 
                     countHelpInfosFound++;
-                    hashtable.Add(helpName, null);
+                    allHelpNames.Add(helpName);
                     yield return helpInfo;
 
                     if ((countHelpInfosFound >= helpRequest.MaxResults) && (helpRequest.MaxResults > 0))
@@ -1053,8 +1053,8 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
 
             int countOfHelpInfoObjectsFound = 0;
             // this is for avoiding duplicate result from help output.
-            Hashtable hashtable = new Hashtable(StringComparer.OrdinalIgnoreCase);
-            Hashtable hiddenCommands = new Hashtable(StringComparer.OrdinalIgnoreCase);
+            var set = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            var hiddenCommands = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
             foreach (string pattern in patternList)
             {
                 CommandSearcher searcher = GetCommandSearcherForSearch(pattern, _context);
@@ -1077,15 +1077,15 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
                         {
                             // this command is not visible to the user (from CommandOrigin) so
                             // dont show help topic for it.
-                            if (!hiddenCommands.ContainsKey(helpName))
+                            if (!hiddenCommands.Contains(helpName))
                             {
-                                hiddenCommands.Add(helpName, null);
+                                hiddenCommands.Add(helpName);
                             }
 
                             continue;
                         }
 
-                        if (hashtable.ContainsKey(helpName))
+                        if (set.Contains(helpName))
                             continue;
 
                         // filter out the helpInfo object depending on user request
@@ -1100,7 +1100,7 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
                             continue;
                         }
 
-                        hashtable.Add(helpName, null);
+                        set.Add(helpName);
                         countOfHelpInfoObjectsFound++;
                         yield return helpInfo;
 
@@ -1130,10 +1130,10 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
 
                         if (helpInfo != null && !string.IsNullOrEmpty(helpName))
                         {
-                            if (hashtable.ContainsKey(helpName))
+                            if (set.Contains(helpName))
                                 continue;
 
-                            if (hiddenCommands.ContainsKey(helpName))
+                            if (hiddenCommands.Contains(helpName))
                                 continue;
 
                             // filter out the helpInfo object depending on user request
@@ -1148,7 +1148,7 @@ internal override IEnumerable<HelpInfo> SearchHelp(HelpRequest helpRequest, bool
                                 continue;
                             }
 
-                            hashtable.Add(helpName, null);
+                            set.Add(helpName);
                             countOfHelpInfoObjectsFound++;
                             yield return helpInfo;