diff --git a/sys/shell/shell.c b/sys/shell/shell.c
index 3ac61e713d..b60338cd22 100644
--- a/sys/shell/shell.c
+++ b/sys/shell/shell.c
@@ -175,7 +175,7 @@ static void handle_input_line(const shell_command_t *command_list, char *line)
             ++argc;
         }
 
-        /* zero out the current position (space or quotation mark) and advance */
+        /* zero out current position (space or quotation mark) and advance */
         if (*pos > 0) {
             *pos = 0;
             ++pos;
@@ -269,10 +269,11 @@ static int readline(char *buf, size_t size)
             return EOF;
         }
 
-        /* We allow Unix linebreaks (\n), DOS linebreaks (\r\n), and Mac linebreaks (\r). */
-        /* QEMU transmits only a single '\r' == 13 on hitting enter ("-serial stdio"). */
-        /* DOS newlines are handled like hitting enter twice, but empty lines are ignored. */
-        /* Ctrl-C cancels the current line. */
+        /* We allow Unix linebreaks (\n), DOS linebreaks (\r\n), and Mac
+         * linebreaks (\r). QEMU transmits only a single '\r' == 13 on hitting
+         * enter ("-serial stdio"). DOS newlines are handled like hitting enter
+         * twice, but empty lines are ignored. Ctrl-C cancels the current line.
+         */
         if (c == '\r' || c == '\n' || c == ETX) {
             if (c == ETX) {
                 curr_pos = 0;
@@ -288,10 +289,12 @@ static int readline(char *buf, size_t size)
             return (length_exceeded) ? -ENOBUFS : curr_pos;
         }
 
-        /* QEMU uses 0x7f (DEL) as backspace, while 0x08 (BS) is for most terminals */
+        /* check for backspace:
+         * 0x7f (DEL) when using QEMU
+         * 0x08 (BS) for most terminals */
         if (c == 0x08 || c == 0x7f) {
             if (curr_pos == 0) {
-                /* The line is empty. */
+                /* ignore empty line */
                 continue;
             }