diff --git a/src/smc.c b/src/smc.c
index 8acbbd8..bbc3b3d 100644
--- a/src/smc.c
+++ b/src/smc.c
@@ -187,7 +187,12 @@ void smc_id(snes_romprops_t* props) {
       }
   }
   if(header->romsize == 0 || header->romsize > 13) {
-    header->romsize = 13;
+    props->romsize_bytes = 1024;
+    header->romsize = 0;
+    while(props->romsize_bytes < file_handle.fsize-1) {
+      header->romsize++;
+      props->romsize_bytes <<= 1;
+    }
   }
   props->ramsize_bytes = (uint32_t)1024 << header->ramsize;
   props->romsize_bytes = (uint32_t)1024 << header->romsize;