diff --git a/lib/std/compress/zstandard/decompress.zig b/lib/std/compress/zstandard/decompress.zig
index fd783e3c9c..68d43c8aeb 100644
--- a/lib/std/compress/zstandard/decompress.zig
+++ b/lib/std/compress/zstandard/decompress.zig
@@ -421,14 +421,14 @@ pub fn decodeZstandardFrameBlocksArrayList(
                 hasher.update(written_slice.second);
             }
         }
-        const added_len = dest.items.len - initial_len;
-        if (frame_context.content_size) |size| {
-            if (added_len != size) {
-                return error.BadContentSize;
-            }
-        }
         if (block_header.last_block) break;
     }
+    const added_len = dest.items.len - initial_len;
+    if (frame_context.content_size) |size| {
+        if (added_len != size) {
+            return error.BadContentSize;
+        }
+    }
 
     if (frame_context.has_checksum) {
         if (src.len < consumed_count + 4) return error.EndOfStream;