diff --git a/lang/cem/libcc.ansi/stdio/doscan.c b/lang/cem/libcc.ansi/stdio/doscan.c
index 8ec2690fd..8c4fffbaa 100644
--- a/lang/cem/libcc.ansi/stdio/doscan.c
+++ b/lang/cem/libcc.ansi/stdio/doscan.c
@@ -174,6 +174,8 @@ _doscan(register FILE *stream, const char *format, va_list ap)
 	long double	ld_val;
 #endif
 
+	if (!*format) return 0;
+
 	while (1) {
 		if (isspace(*format)) {
 			while (isspace(*format))
diff --git a/lang/cem/libcc.ansi/stdio/ungetc.c b/lang/cem/libcc.ansi/stdio/ungetc.c
index dfe5cb125..e78bf265c 100644
--- a/lang/cem/libcc.ansi/stdio/ungetc.c
+++ b/lang/cem/libcc.ansi/stdio/ungetc.c
@@ -19,6 +19,8 @@ ungetc(int ch, FILE *stream)
 	}
 	stream->_count++;
 	p = --(stream->_ptr);		/* ??? Bloody vax assembler !!! */
-	*p = (unsigned char) ch;
+	/* ungetc() in sscanf() shouldn't write in rom */
+	if (*p != (unsigned char) ch)
+		*p = (unsigned char) ch;
 	return ch;
 }