diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index d94e946f4c..6ed1f6c43a 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -129,7 +129,7 @@ static inline void psa_set_key_slot_number(
     psa_key_attributes_t *attributes,
     psa_key_slot_number_t slot_number)
 {
-    attributes->MBEDTLS_PRIVATE(flags) |= MBEDTLS_PSA_KA_FLAG_HAS_SLOT_NUMBER;
+    attributes->MBEDTLS_PRIVATE(has_slot_number) = 1;
     attributes->MBEDTLS_PRIVATE(slot_number) = slot_number;
 }
 
@@ -142,8 +142,7 @@ static inline void psa_set_key_slot_number(
 static inline void psa_clear_key_slot_number(
     psa_key_attributes_t *attributes)
 {
-    attributes->MBEDTLS_PRIVATE(flags) &=
-        ~MBEDTLS_PSA_KA_FLAG_HAS_SLOT_NUMBER;
+    attributes->MBEDTLS_PRIVATE(has_slot_number) = 0;
 }
 
 /** Register a key that is already present in a secure element.
diff --git a/include/psa/crypto_struct.h b/include/psa/crypto_struct.h
index adb33ed214..e8f67d5d59 100644
--- a/include/psa/crypto_struct.h
+++ b/include/psa/crypto_struct.h
@@ -292,6 +292,7 @@ typedef uint16_t psa_key_attributes_flag_t;
 struct psa_key_attributes_s {
 #if defined(MBEDTLS_PSA_CRYPTO_SE_C)
     psa_key_slot_number_t MBEDTLS_PRIVATE(slot_number);
+    int MBEDTLS_PRIVATE(has_slot_number);
 #endif /* MBEDTLS_PSA_CRYPTO_SE_C */
     psa_key_type_t MBEDTLS_PRIVATE(type);
     psa_key_bits_t MBEDTLS_PRIVATE(bits);
@@ -313,7 +314,7 @@ struct psa_key_attributes_s {
 };
 
 #if defined(MBEDTLS_PSA_CRYPTO_SE_C)
-#define PSA_KEY_ATTRIBUTES_MAYBE_SLOT_NUMBER 0,
+#define PSA_KEY_ATTRIBUTES_MAYBE_SLOT_NUMBER 0, 0,
 #else
 #define PSA_KEY_ATTRIBUTES_MAYBE_SLOT_NUMBER
 #endif
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 71535fa914..91f5f16162 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1245,7 +1245,7 @@ psa_status_t psa_get_key_slot_number(
     const psa_key_attributes_t *attributes,
     psa_key_slot_number_t *slot_number)
 {
-    if (attributes->flags & MBEDTLS_PSA_KA_FLAG_HAS_SLOT_NUMBER) {
+    if (attributes->has_slot_number) {
         *slot_number = attributes->slot_number;
         return PSA_SUCCESS;
     } else {