diff --git a/src/resourcefiles/file_zip.cpp b/src/resourcefiles/file_zip.cpp
index 990675dfc..c76bb15f5 100644
--- a/src/resourcefiles/file_zip.cpp
+++ b/src/resourcefiles/file_zip.cpp
@@ -387,7 +387,7 @@ int FZipLump::FillCache()
 
 		case METHOD_SHRINK:
 		{
-			ShrinkLoop((unsigned char *)Cache, LumpSize, Owner->Reader, LumpSize);
+			ShrinkLoop((unsigned char *)Cache, LumpSize, Owner->Reader, CompressedSize);
 			break;
 		}