diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 119b209b..9e032aa3 100755
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -1143,7 +1143,7 @@ enum sexp_context_globals {
 #else
 
 #define sexp_read_char(x, p) (sexp_port_buf(p) ? ((sexp_port_offset(p) < sexp_port_size(p)) ? sexp_port_buf(p)[sexp_port_offset(p)++] : sexp_buffered_read_char(x, p)) : getc(sexp_port_stream(p)))
-#define sexp_push_char(x, c, p) (sexp_port_buf(p) ? (sexp_port_buf(p)[--sexp_port_offset(p)] = ((char)(c))) : ungetc(c, sexp_port_stream(p)))
+#define sexp_push_char(x, c, p) ((c!=EOF) && (sexp_port_buf(p) ? (sexp_port_buf(p)[--sexp_port_offset(p)] = ((char)(c))) : ungetc(c, sexp_port_stream(p))))
 #define sexp_write_char(x, c, p) (sexp_port_buf(p) ? ((sexp_port_offset(p) < sexp_port_size(p)) ? ((((sexp_port_buf(p))[sexp_port_offset(p)++]) = (char)(c)), SEXP_VOID) : sexp_buffered_write_char(x, c, p)) : (putc(c, sexp_port_stream(p)), SEXP_VOID))
 #define sexp_write_string(x, s, p) (sexp_port_buf(p) ? sexp_buffered_write_string(x, s, p) : (fputs(s, sexp_port_stream(p)), SEXP_VOID))
 #define sexp_flush(x, p) (sexp_port_buf(p) ? sexp_buffered_flush(x, p) : (fflush(sexp_port_stream(p)), SEXP_VOID))