diff --git a/src/System.Management.Automation/resources/CatalogStrings.resx b/src/System.Management.Automation/resources/CatalogStrings.resx
index 662b765652b..9235ab84ff6 100644
--- a/src/System.Management.Automation/resources/CatalogStrings.resx
+++ b/src/System.Management.Automation/resources/CatalogStrings.resx
@@ -150,6 +150,9 @@
   <data name="UnKnownCatalogVersion" xml:space="preserve">
     <value>Catalog version is not valid. We only support catalog version {0} and version {1}.</value>
   </data>
+  <data name="WeakCatalogHashAlgorithm" xml:space="preserve">
+    <value>'{0}' is a version 1 catalog that uses SHA1. Consider regenerating this catalog with -CatalogVersion 2.</value>
+  </data>
   <data name="UnableToOpenCatalogDefinitionFile" xml:space="preserve">
     <value>Unable to open catalog definition file.</value>
   </data>
diff --git a/src/System.Management.Automation/security/CatalogHelper.cs b/src/System.Management.Automation/security/CatalogHelper.cs
index 4892f7434e4..ac64e4afbe5 100644
--- a/src/System.Management.Automation/security/CatalogHelper.cs
+++ b/src/System.Management.Automation/security/CatalogHelper.cs
@@ -146,6 +146,20 @@ private static string GetCatalogHashAlgorithm(int catalogVersion)
             return hashAlgorithm;
         }
 
+        /// <summary>
+        /// Emit an advisory warning when using legacy catalog version 1 (SHA-1).
+        /// Advisory only: does not fail catalog generation/validation for compatibility.
+        /// Automation validating catalogs can check CatalogInformation.HashAlgorithm (Test-FileCatalog -Detailed)
+        /// to detect SHA-1 programmatically.
+        /// </summary>
+        private static void WarnIfLegacyCatalogVersion(string catalogFilePath, int catalogVersion)
+        {
+            if (catalogVersion == 1)
+            {
+                _cmdlet.WriteWarning(StringUtil.Format(CatalogStrings.WeakCatalogHashAlgorithm, catalogFilePath));
+            }
+        }
+
         /// <summary>
         /// Generate the Catalog Definition File representing files and folders.
         /// </summary>
@@ -331,6 +345,8 @@ internal static FileInfo GenerateCatalog(PSCmdlet cmdlet, Collection<string> Pat
             _cmdlet = cmdlet;
             string hashAlgorithm = GetCatalogHashAlgorithm(catalogVersion);
 
+            WarnIfLegacyCatalogVersion(catalogFilePath, catalogVersion);
+
             if (!string.IsNullOrEmpty(hashAlgorithm))
             {
                 // Generate Path for Catalog Definition File
@@ -733,6 +749,8 @@ internal static CatalogInformation ValidateCatalog(PSCmdlet cmdlet, Collection<s
             Dictionary<string, string> catalogHashes = GetHashesFromCatalog(catalogFilePath, excludedPatterns, out catalogVersion);
             string hashAlgorithm = GetCatalogHashAlgorithm(catalogVersion);
 
+            WarnIfLegacyCatalogVersion(catalogFilePath, catalogVersion);
+
             if (!string.IsNullOrEmpty(hashAlgorithm))
             {
                 Dictionary<string, string> fileHashes = CalculateHashesFromPath(catalogFolders, catalogFilePath, hashAlgorithm, excludedPatterns);