diff --git a/boot/zephyr/include/config-asn1.h b/boot/zephyr/include/config-asn1.h
index e772ceb..25d33fb 100644
--- a/boot/zephyr/include/config-asn1.h
+++ b/boot/zephyr/include/config-asn1.h
@@ -40,7 +40,7 @@
 // #define MBEDTLS_BIGNUM_C
 // #define MBEDTLS_MD_C
 // #define MBEDTLS_OID_C
-#define MBEDTLS_SHA256_C
+// #define MBEDTLS_SHA256_C
 
 #include "mbedtls/check_config.h"
 
diff --git a/boot/zephyr/prj-p256.conf b/boot/zephyr/prj-p256.conf
index a3cf7c0..5bea3d0 100644
--- a/boot/zephyr/prj-p256.conf
+++ b/boot/zephyr/prj-p256.conf
@@ -9,6 +9,7 @@
 CONFIG_MBEDTLS_CFG_FILE="config-asn1.h"
 CONFIG_TINYCRYPT=y
 CONFIG_TINYCRYPT_ECC_DSA=y
+CONFIG_TINYCRYPT_SHA256=y
 
 ### mbedTLS wants a heap
 CONFIG_HEAP_MEM_POOL_SIZE=16384