diff --git a/sys/include/riotboot/slot.h b/sys/include/riotboot/slot.h
index 93a38b16f0..c08b6e27d4 100644
--- a/sys/include/riotboot/slot.h
+++ b/sys/include/riotboot/slot.h
@@ -104,6 +104,27 @@ size_t riotboot_slot_offset(unsigned slot);
  */
 void riotboot_slot_dump_addrs(void);
 
+/**
+ * @brief  Get the size of a slot
+ *
+ * @param[in]   slot    slot nr to get the size from
+ *
+ * @returns             The slot size in bytes
+ */
+static inline size_t riotboot_slot_size(unsigned slot)
+{
+    switch(slot) {
+        case 0:
+            return SLOT0_LEN;
+#if NUM_SLOTS==2
+        case 1:
+            return SLOT1_LEN;
+#endif
+        default:
+            return 0;
+    }
+}
+
 /**
  * @brief   Number of configured firmware slots (incl. bootloader slot)
  */
diff --git a/sys/riotboot/flashwrite.c b/sys/riotboot/flashwrite.c
index f3f26b5b9f..e51cb341b8 100644
--- a/sys/riotboot/flashwrite.c
+++ b/sys/riotboot/flashwrite.c
@@ -34,15 +34,10 @@ static inline size_t min(size_t a, size_t b)
     return a <= b ? a : b;
 }
 
-size_t riotboot_flashwrite_slotsize(const riotboot_flashwrite_t *state)
+size_t riotboot_flashwrite_slotsize(
+        const riotboot_flashwrite_t *state)
 {
-    switch (state->target_slot) {
-        case 0: return SLOT0_LEN;
-#if NUM_SLOTS==2
-        case 1: return SLOT1_LEN;
-#endif
-        default: return 0;
-    }
+    return riotboot_slot_size(state->target_slot);
 }
 
 int riotboot_flashwrite_init_raw(riotboot_flashwrite_t *state, int target_slot,