diff --git a/boot/bootutil/include/bootutil/enc_key.h b/boot/bootutil/include/bootutil/enc_key.h
index d2477ca..0f4ab57 100644
--- a/boot/bootutil/include/bootutil/enc_key.h
+++ b/boot/bootutil/include/bootutil/enc_key.h
@@ -20,6 +20,7 @@
 #ifndef BOOTUTIL_ENC_KEY_H
 #define BOOTUTIL_ENC_KEY_H
 
+#include <stdbool.h>
 #include <flash_map_backend/flash_map_backend.h>
 #include "mcuboot_config/mcuboot_config.h"
 #include "bootutil/image.h"
@@ -51,7 +52,7 @@
 int boot_enc_set_key(uint8_t slot, uint8_t *enckey);
 int boot_enc_load(const struct image_header *hdr, const struct flash_area *fap,
         uint8_t *enckey);
-int boot_enc_valid(const struct flash_area *fap);
+bool boot_enc_valid(const struct flash_area *fap);
 void boot_encrypt(const struct flash_area *fap, uint32_t off, uint32_t sz,
         uint32_t blk_off, uint8_t *buf);
 void boot_enc_zeroize(void);
diff --git a/boot/bootutil/src/encrypted.c b/boot/bootutil/src/encrypted.c
index 13ba2f4..6ac10d6 100644
--- a/boot/bootutil/src/encrypted.c
+++ b/boot/bootutil/src/encrypted.c
@@ -306,7 +306,7 @@
     return rc;
 }
 
-int
+bool
 boot_enc_valid(const struct flash_area *fap)
 {
     int rc;
@@ -315,7 +315,7 @@
     if (rc < 0) {
         /* can't get proper slot number - skip encryption, */
         /* postpone the erro for a upper layer */
-        return 0;
+        return false;
     }
 
     return enc_state[rc].valid;