PowerShell
diff --git a/‎src/System.Management.Automation/engine/LanguagePrimitives.cs
+4-10 b/‎src/System.Management.Automation/engine/LanguagePrimitives.cs
+4-10
diff --git a/‎test/powershell/engine/Api/LanguagePrimitive.Tests.ps1
+38 b/‎test/powershell/engine/Api/LanguagePrimitive.Tests.ps1
+38
@@ -202,7 +202,6 @@ public override object ConvertFrom(object sourceValue, Type destinationType, IFo
             string sourceAsString = (string)LanguagePrimitives.ConvertTo(sourceValue, typeof(string), formatProvider);
             return LanguagePrimitives.ConvertTo(sourceAsString, destinationType, formatProvider);
         }
-
         /// <summary>
         /// Returns false, since this converter is not designed to be used to
         /// convert from the type associated with the converted to other types.
@@ -2943,17 +2942,12 @@ private static object ConvertStringToInteger(
                     return result;
                 }
 
-                if (resultType == typeof(BigInteger))
-                {
-                    // Fallback for BigInteger: manual parsing using any common format.
-                    NumberStyles style = NumberStyles.AllowLeadingSign
-                        | NumberStyles.AllowDecimalPoint
-                        | NumberStyles.AllowExponent
-                        | NumberStyles.AllowHexSpecifier;
-
+               if (resultType == typeof(BigInteger))
+               { 
+                    NumberStyles style = NumberStyles.Integer | NumberStyles.AllowThousands;
+                    
                     return BigInteger.Parse(strToConvert, style, NumberFormatInfo.InvariantInfo);
                 }
-
                 // Fallback conversion for regular numeric types.
                 return GetIntegerSystemConverter(resultType).ConvertFrom(strToConvert);
             }
 
@@ -185,4 +185,42 @@ Describe "Language Primitive Tests" -Tags "CI" {
         $test.TestHandlerReturnEnum() | Should -BeTrue
         $test.TestHandlerReturnObject() | Should -BeTrue
     }
+    
+    It 'Handles large numbers with thousands separators that previously failed' {
+        $formattedNumber = "9223372036854775,807"
+        $convertedValue = [System.Management.Automation.LanguagePrimitives]::ConvertTo($formattedNumber, [bigint])
+        $convertedValue | Should -Be 9223372036854775807
+    }
+
+    It 'Handles extremely large numbers to verify precision' {
+        $formattedNumber = "99999999999999999999999999999"
+        $convertedValue = [System.Management.Automation.LanguagePrimitives]::ConvertTo($formattedNumber, [bigint])
+        $convertedValue | Should -Be 99999999999999999999999999999
+    }
+
+    It 'Parses mixed separators correctly' {
+        $formattedNumber = "1,0000,00"
+        $convertedValue = [System.Management.Automation.LanguagePrimitives]::ConvertTo($formattedNumber, [bigint])
+        $convertedValue | Should -Be 1000000
+    }
+
+    It 'Parses a number string using the invariant culture, irrespective of the current culture' {
+        $originalCulture = [cultureinfo]::CurrentCulture
+        try {
+            [cultureinfo]::CurrentCulture = [cultureinfo]::GetCultureInfo("de-DE")
+            $formattedNumber = "1.000"  # in de-DE this means 1000
+            $convertedValue = [System.Management.Automation.LanguagePrimitives]::ConvertTo($formattedNumber, [bigint])
+            # since [bigint] uses invariant culture, this will be parsed as 1
+            $convertedValue | Should -Be 1
+        }
+        finally {
+            [cultureinfo]::CurrentCulture = $originalCulture
+        }
+    }
+
+    It 'Casts from floating-point number string to BigInteger using fallback' {
+        $formattedNumber = "1.2"
+        $convertedValue = [System.Management.Automation.LanguagePrimitives]::ConvertTo($formattedNumber, [bigint])
+        $convertedValue | Should -Be 1
+    }
 }