diff --git a/g3/pbm2g3.c b/g3/pbm2g3.c
index b188b81..54a6386 100644
--- a/g3/pbm2g3.c
+++ b/g3/pbm2g3.c
@@ -448,6 +448,12 @@ int main _P2( (argc, argv), int argc, char ** argv )
exit(4);
}
+ if ( pbm_xsize <= 0 || pbm_ysize <= 0 )
+ {
+ fprintf( stderr, "%s: malformed PBM file (negative width or height)\n", argv[0] );
+ exit(4);
+ }
+
/* unsupported bitmap types */
if ( pbm_type == pgm || pbm_type == pgm_raw )