--- clamav-0.88.7.orig/libclamav/fsg.c
+++ clamav-0.88.7/libclamav/fsg.c
@@ -72,7 +72,8 @@
   char *csrc = source, *cdst = dest;
   int oob, lostbit = 1;
 
-  /* I assume buffers size is >0 - No checking! */
+  if (ssize<=0 || dsize<=0) return -1;
+
   *cdst++=*csrc++;
 
   while ( 1 ) {