diff --git a/src/libraries/Common/src/System/Text/OSEncoding.Windows.cs b/src/libraries/Common/src/System/Text/OSEncoding.Windows.cs
index fc3f866ec96a6..4d3d91e423e45 100644
--- a/src/libraries/Common/src/System/Text/OSEncoding.Windows.cs
+++ b/src/libraries/Common/src/System/Text/OSEncoding.Windows.cs
@@ -168,7 +168,7 @@ public override int GetMaxCharCount(int byteCount)
         {
             ArgumentOutOfRangeException.ThrowIfNegative(byteCount);
 
-            long charCount = byteCount * 4; // Max possible value for all encodings
+            long charCount = (long)byteCount * 4; // Max possible value for all encodings
 
             if (charCount > 0x7fffffff)
                 throw new ArgumentOutOfRangeException(nameof(byteCount), SR.ArgumentOutOfRange_GetCharCountOverflow);