diff --git a/sys/include/isrpipe.h b/sys/include/isrpipe.h
index f9bf0460c4..df2fde7439 100644
--- a/sys/include/isrpipe.h
+++ b/sys/include/isrpipe.h
@@ -52,7 +52,7 @@ typedef struct {
  * @param[in]   buf         buffer to use as ringbuffer (must be power of two sized!)
  * @param[in]   bufsize     size of @p buf
  */
-void isrpipe_init(isrpipe_t *isrpipe, char *buf, size_t bufsize);
+void isrpipe_init(isrpipe_t *isrpipe, uint8_t *buf, size_t bufsize);
 
 /**
  * @brief   Put one character into the isrpipe's buffer
@@ -63,7 +63,7 @@ void isrpipe_init(isrpipe_t *isrpipe, char *buf, size_t bufsize);
  * @returns     0 if character could be added
  * @returns     -1 if buffer was full
  */
-int isrpipe_write_one(isrpipe_t *isrpipe, char c);
+int isrpipe_write_one(isrpipe_t *isrpipe, uint8_t c);
 
 /**
  * @brief   Read data from isrpipe (blocking)
@@ -74,7 +74,7 @@ int isrpipe_write_one(isrpipe_t *isrpipe, char c);
  *
  * @returns     number of bytes read
  */
-int isrpipe_read(isrpipe_t *isrpipe, char *buf, size_t count);
+int isrpipe_read(isrpipe_t *isrpipe, uint8_t *buf, size_t count);
 
 #ifdef __cplusplus
 }
diff --git a/sys/include/isrpipe/read_timeout.h b/sys/include/isrpipe/read_timeout.h
index f37947f19a..984de0c53f 100644
--- a/sys/include/isrpipe/read_timeout.h
+++ b/sys/include/isrpipe/read_timeout.h
@@ -44,7 +44,7 @@ extern "C" {
  * @returns     number of bytes read
  * @returns     -ETIMEDOUT on timeout
  */
-int isrpipe_read_timeout(isrpipe_t *isrpipe, char *buf, size_t count, uint32_t timeout);
+int isrpipe_read_timeout(isrpipe_t *isrpipe, uint8_t *buf, size_t count, uint32_t timeout);
 
 /**
  * @brief   Read data from isrpipe (with timeout, blocking, wait until all read)
@@ -60,7 +60,7 @@ int isrpipe_read_timeout(isrpipe_t *isrpipe, char *buf, size_t count, uint32_t t
  * @returns     number of bytes read
  * @returns     -ETIMEDOUT on timeout
  */
-int isrpipe_read_all_timeout(isrpipe_t *isrpipe, char *buf, size_t count, uint32_t timeout);
+int isrpipe_read_all_timeout(isrpipe_t *isrpipe, uint8_t *buf, size_t count, uint32_t timeout);
 
 #ifdef __cplusplus
 }
diff --git a/sys/isrpipe/isrpipe.c b/sys/isrpipe/isrpipe.c
index 9b8ce170d9..cb01b5b807 100644
--- a/sys/isrpipe/isrpipe.c
+++ b/sys/isrpipe/isrpipe.c
@@ -19,13 +19,13 @@
 
 #include "isrpipe.h"
 
-void isrpipe_init(isrpipe_t *isrpipe, char *buf, size_t bufsize)
+void isrpipe_init(isrpipe_t *isrpipe, uint8_t *buf, size_t bufsize)
 {
     mutex_init(&isrpipe->mutex);
-    tsrb_init(&isrpipe->tsrb, (uint8_t *)buf, bufsize);
+    tsrb_init(&isrpipe->tsrb, buf, bufsize);
 }
 
-int isrpipe_write_one(isrpipe_t *isrpipe, char c)
+int isrpipe_write_one(isrpipe_t *isrpipe, uint8_t c)
 {
     int res = tsrb_add_one(&isrpipe->tsrb, c);
 
@@ -37,11 +37,11 @@ int isrpipe_write_one(isrpipe_t *isrpipe, char c)
     return res;
 }
 
-int isrpipe_read(isrpipe_t *isrpipe, char *buffer, size_t count)
+int isrpipe_read(isrpipe_t *isrpipe, uint8_t *buffer, size_t count)
 {
     int res;
 
-    while (!(res = tsrb_get(&isrpipe->tsrb, (uint8_t *)buffer, count))) {
+    while (!(res = tsrb_get(&isrpipe->tsrb, buffer, count))) {
         mutex_lock(&isrpipe->mutex);
     }
     return res;
diff --git a/sys/isrpipe/read_timeout/read_timeout.c b/sys/isrpipe/read_timeout/read_timeout.c
index b33a9cbfda..d009131ffc 100644
--- a/sys/isrpipe/read_timeout/read_timeout.c
+++ b/sys/isrpipe/read_timeout/read_timeout.c
@@ -35,7 +35,7 @@ static void _cb(void *arg)
     mutex_unlock(_timeout->mutex);
 }
 
-int isrpipe_read_timeout(isrpipe_t *isrpipe, char *buffer, size_t count, uint32_t timeout)
+int isrpipe_read_timeout(isrpipe_t *isrpipe, uint8_t *buffer, size_t count, uint32_t timeout)
 {
     int res;
 
@@ -44,7 +44,7 @@ int isrpipe_read_timeout(isrpipe_t *isrpipe, char *buffer, size_t count, uint32_
     xtimer_t timer = { .callback = _cb, .arg = &_timeout };
 
     xtimer_set(&timer, timeout);
-    while (!(res = tsrb_get(&isrpipe->tsrb, (uint8_t *)buffer, count))) {
+    while (!(res = tsrb_get(&isrpipe->tsrb, buffer, count))) {
         mutex_lock(&isrpipe->mutex);
         if (_timeout.flag) {
             res = -ETIMEDOUT;
@@ -57,9 +57,9 @@ int isrpipe_read_timeout(isrpipe_t *isrpipe, char *buffer, size_t count, uint32_
 }
 
 
-int isrpipe_read_all_timeout(isrpipe_t *isrpipe, char *buffer, size_t count, uint32_t timeout)
+int isrpipe_read_all_timeout(isrpipe_t *isrpipe, uint8_t *buffer, size_t count, uint32_t timeout)
 {
-    char *pos = buffer;
+    uint8_t *pos = buffer;
 
     while (count) {
         int res = isrpipe_read_timeout(isrpipe, pos, count, timeout);